or is it cheaper to replace

I don't know if any commercial outfit does it, but you can purchase individual parts for everything & get them from Mercruiserparts.com. I't sot of difficult to find the parts breakdown as it is not in the regular sections. You must look under some of the performance areas at the bottom of the list. I fixed several leaks in my pumps with parts ordered (new o-rings, screws, etc) They worked perfectly. Easy to do but a little messy.
Hydraulics really aren't that difficult unless you have to design a system. I'm sire many o-rings & seals could be purchased at a local hydraulics shop also cheaper, too. Many pumps are on ebay, but all at $200.00. O-rings are far cheaper!

does anyone offer a compleat rebuild kit for them? One of mine sounds like it is pumping air all the time. It does not react as fast as the other side that sounds normal.

I replaced all of the O rings in both of mine. there was a lot of dirt and sludge in both of them. A thorough cleaning and new o rings will do wonders for them.

Once I bought a complete rebuild kit for an outboard pump. Had every gasket, oring, check valve, and the plastic manual override valve. Cost around $25. Took less than an hour to do the whole shebang. Don't know if a "kit" like that is available for the offshore pumps but it might be.

I've had 2 motors rebuilt as well (for about $25 each).

I take mine to my guy that rebuilds my Alternators. He charges me 80 bucks if I remember correctly. Seems to do the trick. New ones are like 350 bucks so as long as you did not really smoke it you should be ok. I would call around to you local alt. rebuilder.

Jon

merc no longer has the rebuild kits....sucks...i had to buy the complete pump...i hope this is a temporary thing..