sounds like you have a few more things to check, but are a heck of a lot better off than when the shop told you that you needed all those parts. What does the sight glass look like when you run? Do you have any leaking past the monovalve adding heat to the heater core? Also, I've never done this but I bet it works: put chalk marks on the triangular plate and compressor body. Hook a timing light to any convenient gasser and point it at compressor. Fool with idle speed of 1 or both engines to "freeze" motion. You'll probably see if the clutch is slipping. If it's not slipping (a tiny bit is OK), don't fix it!

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.