My experience with a rebuilt R4, actually two of them was a nightmare that ended in my wife getting rid of an otherwise outstanding 300TD. I worked my ___ off in the raging heat trying to overcome the mess put throughout the system, and ultimately it beat me. Don't go through what I did.
I know how it is when money is tight, but find a NEW R4 at the best price you can find. A rebuilt compressor is false economy.
There is one other thing that would be worthwhile to do if you can find out more about it. After I went through that nightmare, I heard someone mention a suction side inline filter. It would definitely be worth consulting an automotive air conditioning supply house to learn about this. It would ensure that none of the junk in the system put there by a previously failed compressor would reach the new compressor. I think if you used a new compressor and one of these filters, you would probably have a permanent repair.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in