Re: 1988 3.0 gs
Volvo is B/O on that pump. Do you have a cross reference to another pump? No luck with Jabsco or Sherwood. Maybe Johnson?
I'm here to tell you that, to my limited knowledge, there isn't an aftermarket pump. I have the same engine in a 1995 flavor that is going back in the boat tomorrow. Rebuilt the engine and replaced water pump also. $300 just seems ridiculously expensive for a water pump, but I decided I would rather have something that would last than a cheapo Sierra, and that I KNOW is the correct pump.
P.S. my engine is one that someone was monkeying around with before I got a hold of it. Having to fix a lot of "shade tree" mistakes. Not to say I'm perfect, but who buys a new block, and reuses gaskets??