I ordered a service kit from Mermaid Marine for my elderly Pac 22. In the box that arrived was some filters, o-rings, belts and an impeller complete with gaskets.
Having removed oil / air coolers I set about changing the impeller.
Not only was the impeller a bugger to get to (considering it is a consumable), it bears no resemblance to what I was expecting or what I was sent.
It's made by a firm called Gilkes in Kendal and is obviously the reason why you can run these things out of the water for a short time without damaging the impeller pump.
There's nothing to change other than the o-ring.
There is some nice engineering on these old Pac 22's.