Hi Grant,
Thanks for the info. I've been searching the old postings and have narrowed it down to a fitted filter on Chevrolet compressors and the inverted 'v' inlet on Ford compressors.
http://www.mapleleafup.net/forums/sh...ght=compressor
I think the attached photo of a transmission breather for CMP could be a close relative of the part, but it would be nice to have something a bit more definite!