I have had no end of trouble with the $400 rebuilt unit. You have to take the speed control thingy off your old one, and I think the manfold pipe connector as well. I have not been able to get the speed control to seal right despite two shop visits.
If you are going to this much trouble, get the new compressor.
Think you also need a drier bottle and you might want to check to see if you have the higher temp/pressure switches.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe