Running in fresh water would it matter if a automotive pump was used instead of a marine?

Yes, the marine should have different bearings/seals/shaft/backing plate for non-antifreeze , and more importantly salt water, use.

A good quality marine recirc pump should last almost indefinately in a fresh water boat. They do go, but, I take care of several early 90's and late 80's boats that still have the stocker. Older boats that get laid up for a few years seem to be the one's that go. Juts what I see, again on (very) fresh water..

Anyone know if they are rebuildable or if anyone offers a rebuilt unit?

Put on a crossover much better looking, one less thing to go bad, and up to 10hp gain. have a set up in swap shop everything you need to bolt on ,,belts, hoses all work done for you.

the std automotive one will rust to crap..even in fresh water..ok to use with closed system w/antifreeze...

Automotive pumps are designed to run with lubrication from the antifreeze. If you run them with straight water the seals will burn out and leak. Learned that one the hard way.

Thanks...that's what I was trying to avoid

be careful,most modern gm circulating pumps are driven in reverse rotation,they are different

most all of the "marine" one's are Bi-directional now