...but "old" seals.

By that I mean those compressors were more than likely stored for a very long time in such a fashion that their "pre-oil" (if they ever even had any) drained away from the seals in question leaving them high, dry, and shrunken.

The guys at my local parts place have confirmed that this is becoming a real problem with new and reman R4 and A6 compressors that don't sell like they used to. They suggest to their customers basically flooding new compressors with oil for a few days and leaving them so orientated as to moisten, soften, swell and re-condition the seals.

The usual disclaimers apply to the following redneck fix.

Add a single drop or maybe two of brake fluid to the flood oil to swell and soften those seals.

Hope this helps...