Sounds like the truck is important to you so don't let that lazy non bill paying SOB get his hands back on it at any price, payed by you, OR your friends.
Like it or not the oil leaks are just symptomatic of the real problem, basically lack of knowledge, poor work ethic, and lousy craftsmanship. Idiot mechanics will, not if, cost you a motor.
The only way to even begin knowing where you are at, is to pull the pan and rear main cap, throw a dial indicator on the rear main, and spin the motor. I personally wouldn't feel comfortable with anything less than taking the motor to a well equipped, reputable machine shop and have them mic the crank and check it for straightness. Don't forget to have the crank to block endplay checked too, because a bad thrust bearing, or out of spec thrust bearing faces on the crank can be a cause of the rear main seal leaking. Have them check the line bore of the main bearing saddles while they've got it apart, too. Even if they didn't find anything wrong but poorly installed seals and gaskets, at least you'd know, and could have them properly put it back together, although at that point it might be cost effective to overhaul at least the short block.
Just make sure to find someone you really trust to work on it if you can't or just don't have the time to tear it apart yourself.