You have to kinda gustimate how much oil to put into your old compressor.Got
oil stains and accumulated dirt around the compressor(leaking oil attracts
this dust)??  Same for the hose connections? Unknown history??Was your
system ever so low the low pressue cut off switch shut the system down??
More than once, you say! Stick about 2 ounces in for good measure, anyway.
Won't hurt nothin'. The oil that leaves the compressor seems to wind up in
the evaperator. If the compressor is making a racket and, a shot of oil
quiets it down maybe add a bit more.

In early Vanagons, VW satisfied the lack of a low pressure cut off switch by
adding a sentence to the owners manuel- "Be sure to take your Vanagon to the
dealer and have the A/C system checked out before each cooling season". It
is the loss of refrigerant pressures that cause the oil to leave the
compressor. I guess this didn't work,so they added the switch in '86.

 The Sanden web site shows how to make a dip stick to measure, but got to
discharge your system and remove the compressor from its mounts--first. If
you want to do it right.  Maybe  www.sanden.com

Once , I went to an A/C speciality shop and picked the owners brain. When I
asked which tools (and how hard) were needed for changing out the clutch
/pulley, he answered that he had never done it before. He said that he
changes the compressor. Nobody he was aware of changed the clutch pulley. I
think it was a $$$$$ issue, and when it is 98 degrees and humid, few would
complain.

I say to get the Bus Depot compressor because their supplier is the best.
New compressors have a shelf life of 18 months. If they are not installed,
they are junk. The shaft seal has shrunk up and will leak. This supplier
knows that and stands behind all his compressors. He calls them back and
will ( he changes clutch/pulleys)put in a new seal.