Yes, the base gasket seals it there, but underneath the casting is a seal and washer that the long inlet pipe I guess push fits into.
I had an idea in the hour before dawn that the under skeg pickup may have been partially blocked, kinked or damaged somehow. Dropped the gearbox and pulled the pump apart again, removed the screen and pushed a rod up it, no obstruction, but plenty of holes / corrosion once I looked closer. Spoke to an old-school Chrysler guy who said it was a common fault as the thin ali pipes used to corrode and cause pumping issues by drawing in air.
