Those are not zerks - they are studs, covered with so much grunge you can't determine what they are. Anyway - you must check your front axle vent, as a clogged vent (and the crappy factory design) will pressurize the axle and cause leaks such as this.
What I have done (and there are other methods) is to simply pry off the floating axle vent cap (the part that wiggles) with a screwdriver, remove the spring and rubber disk, and slide on a 3' section of 3/8" fuel line over the remaining nipple that projects from the axle. Clamp it with an appropriate hose clamp, and run the hose well up high into the engine compartment where it's not exposed to wheel splash. Push a fuel filter into the end of the hose, if you like.
The reason the factory design is poor is that the rubber disk gets coated with gear oil, and then effectively glues itself to the vent, and the axle can no longer breathe properly. This can cause pinion seal leaks, too.
After all this, wipe down the entire knuckle area with a cloth and then watch for leaks. Your birfield cavities may now be full of birfield soup, and the knuckles will simply weep oil until you completely repack the front axle.
Get a front axle manual ($OR sells one) and read up on the entire axle.
