There are injection tools (I have one) that would keep the system sealed, otherwise you'd have to evacuate, add just oil and recharge, or oil with refrigerant. Adding oil to a system that has remained closed is a guessing game on how much to add. Too much, as you may know, will reduce the efficiency.

Maybe the shaft bearing/sleeve is worn?? Try removing the drive belt and pull/push/shack the pulley to see if it has excessive play. You may need to lock the clutch with 12v jumper.

Here's a site where parts may be available:
http://www.acsource.com/index.aspx

I've dealt with them and they are very reputable.