4.3L V6 engine uses a Harrison HT6. The 2.2L 4 cyl engines use H6. Very common, (as in they all do it) for them to develop a leak where the case halves come together. Usually on the bottom where you can't see it without removing it. Sanden makes a different design compressor and doesn't have this problem, and it's much quieter than the Harrison.
Harrison HT6 compressor:
Sanden compressor:
