Hardly anyone keeps service records on vehicles anymore and the newest 80 is now over 20 years old. The oldest are approaching 30 years.
Anyone contemplating purchasing any vehicle over 20 years of age, should just count on baselining everything. The quicker the better. Parts are not going to get any easier to acquire.
Rust will always be a killer. Sure, it can be repaired, but not in a cost or time effective manner. Major rust would be the only reason to walk away from a great deal on an 80.
Unless you’re purchasing from a fellow trusted Mud member who you know handles the maintenance properly, then just count on replacing that front seal, the oil pump cover seal, distributor o-ring, etc...
Then while you’re there, you might as well go through and replace belts and hoses. A new radiator might be a good idea too.
Knuckles are pretty easy to verify, they’re either too wet or too dry, so chances are you’ll be addressing those as well.
Also, if you’re looking at an 80 that doesn’t have the CEL glowing, then someone more than likely removed the bulb. Have the codes scanned. The guy I bought my 80 from had the codes cleared before I came to pickup the truck. When the light came on after a few miles, I wasn’t surprised at all.
Buy an 80 as cheap as you can, because the money you spend after the sale, will more than likely top the price you paid for the truck.