I smear a bit of fuel on the seal before assembling - don't know if it will help in this instance though.

By CAV-style, do you mean a copy - one of those generic no-name housings that's painted light grey?

When I was doing my conversion, that was the first thing I bought, but as soon as I really examined it and saw the cheap looking build quality I returned it. Sales guy tried telling me it was a genuine Delphi - the filter that came with it did have Delphi printed on it (although in very poor print quality so I have my doubts), but the housing was definitely not.

I noticed you're in Vic. Are you in Melbourne? BSP Diesel in Campbellfield sell the genuine Delphi CAV assemblies for only about $15 more than the cheap copies. Seeing as they also give you 2 brass hose tails, it ends up being around the same price.

Maybe give that a try, money permitting?