Looking over this thread (kind of fast). A few things come to mind.
Brakes:
One rear caliper piston going bad is not common. Unless not properly service over vehicles life (flush/bleed). Old fluid, once factory fill has been replaced. Must be flushed every 2 to 3 years. Not flushing regularly and piston may become damaged (pitted), due to moisture content in fluid. But all 4 calipers would likely have damage. The number 1 reason rear calipers need R&R: The rubber bleeder caps are not sealing out water. Either cap missing or way past useful life. Then bleeder freeze in, and that caliper is never flushed/bleed.
Could be, they found slide pins frozen in torque plate of 1 rear caliper. The reason a slide pin freezes in, is it's boots not fitted tightly. Which allows water in. Why because past useful life (typically best to R&R boots, every other brake pad service) or they just weren't seated properly. Water get in slide pin area and they freeze. I suppose a foreign object could also damage a slide boot, but I've not seen happen.
All the above condition are preventable, with proper serving & inspecting.
FDS boots:
Front drive shaft boots (Which each FDS has 2 CV's and 3 axles (AKA CV)), very often weep from under the clamp. Most common is at the inner boot small (outer) clamp. These can simple be re- clamped. If boot has a hole or rip, it must be replaced. Before I replace any boots, I look very close at the health of FDS. If either CV has remarkable play, axle splines excessively worn or groove for snap ring enlarged or rounded. Then I'd not reboot, I'd replace the FDS. At 200K miles likely money is better money spent on new OEM FDS.
Typical boot weep from under clamp:
Rear main seal:
Rear main seal leak is not common in properly maintain 4.7L. Which means regular oil & filter service. But one thing that will cause rear main seal leak, and most every rubber seal to leak. HM (high Mileage) oil. HM oil is BAD stuff that should never be used.
Inspection of rear oil leak. Is done first by getting a picture of weep hole at bottom of bellhousing. Than cleaning and get a clean picture for comparison and no mistake is was clean of oil. Drive and keep motoring for leaks reappearance.
Machine Turning rotors:
Personally, I'm big on turning rotors. Especially the fronts. Turning done right, eliminates pulling, steering wheel pulsing and often noisy brakes. It also increases pad life IMHO, if any scoring/grooving was present. Some think, turning casual wear-out (hitting limits) of rotors faster. I disagree. Rotors groove, scored, hot spot, etc. tend to wear faster and yield poor braking. Additional you don't want rotor on too long. What's too long; when rotor disk separate at cooling fins between disk, from corrosion. I've gotten 90K miles with combo of City, HWY and mountain driving on front pads with turned rotors. I can usually get 3 sets of pads on same OEM rotors.
Turning done properly also removes run-out. With new Toyota OEM rotors, run-out is not often out of spec, but can be improved by FSM run-out procedure. Even new OEM should have run out checked and set. This is time consuming on rear. So time consuming on fronts, it's impractical to set. Turning rotor On The Vehicles (OTV) lathe, corrects run-out and turns to the hubs.
Here aftermarket rotors with OEM pads, both relatively new (~30K miles). Driver was using brakes to control downhill speed (bad habit). This causes brakes to get very hot and can catch them on fire
It's also where run-out being out, really shows up with steering wheel pulse.
OTV turning corrected steering wheel pulse issue on above (video) 100 series.
Brakes:
One rear caliper piston going bad is not common. Unless not properly service over vehicles life (flush/bleed). Old fluid, once factory fill has been replaced. Must be flushed every 2 to 3 years. Not flushing regularly and piston may become damaged (pitted), due to moisture content in fluid. But all 4 calipers would likely have damage. The number 1 reason rear calipers need R&R: The rubber bleeder caps are not sealing out water. Either cap missing or way past useful life. Then bleeder freeze in, and that caliper is never flushed/bleed.
Could be, they found slide pins frozen in torque plate of 1 rear caliper. The reason a slide pin freezes in, is it's boots not fitted tightly. Which allows water in. Why because past useful life (typically best to R&R boots, every other brake pad service) or they just weren't seated properly. Water get in slide pin area and they freeze. I suppose a foreign object could also damage a slide boot, but I've not seen happen.
All the above condition are preventable, with proper serving & inspecting.
FDS boots:
Front drive shaft boots (Which each FDS has 2 CV's and 3 axles (AKA CV)), very often weep from under the clamp. Most common is at the inner boot small (outer) clamp. These can simple be re- clamped. If boot has a hole or rip, it must be replaced. Before I replace any boots, I look very close at the health of FDS. If either CV has remarkable play, axle splines excessively worn or groove for snap ring enlarged or rounded. Then I'd not reboot, I'd replace the FDS. At 200K miles likely money is better money spent on new OEM FDS.
Typical boot weep from under clamp:
Rear main seal:
Rear main seal leak is not common in properly maintain 4.7L. Which means regular oil & filter service. But one thing that will cause rear main seal leak, and most every rubber seal to leak. HM (high Mileage) oil. HM oil is BAD stuff that should never be used.
Inspection of rear oil leak. Is done first by getting a picture of weep hole at bottom of bellhousing. Than cleaning and get a clean picture for comparison and no mistake is was clean of oil. Drive and keep motoring for leaks reappearance.
Machine Turning rotors:
Personally, I'm big on turning rotors. Especially the fronts. Turning done right, eliminates pulling, steering wheel pulsing and often noisy brakes. It also increases pad life IMHO, if any scoring/grooving was present. Some think, turning casual wear-out (hitting limits) of rotors faster. I disagree. Rotors groove, scored, hot spot, etc. tend to wear faster and yield poor braking. Additional you don't want rotor on too long. What's too long; when rotor disk separate at cooling fins between disk, from corrosion. I've gotten 90K miles with combo of City, HWY and mountain driving on front pads with turned rotors. I can usually get 3 sets of pads on same OEM rotors.
Turning done properly also removes run-out. With new Toyota OEM rotors, run-out is not often out of spec, but can be improved by FSM run-out procedure. Even new OEM should have run out checked and set. This is time consuming on rear. So time consuming on fronts, it's impractical to set. Turning rotor On The Vehicles (OTV) lathe, corrects run-out and turns to the hubs.
Here aftermarket rotors with OEM pads, both relatively new (~30K miles). Driver was using brakes to control downhill speed (bad habit). This causes brakes to get very hot and can catch them on fire
It's also where run-out being out, really shows up with steering wheel pulse.
OTV turning corrected steering wheel pulse issue on above (video) 100 series.
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