Does it like to blow alot of smoke at start up? Gm got bars leaks to make they're gm seal tabs, which is used at factory.
http://www.barsproducts.com/product.cfm?id=37 Like this one....
If your wanting to get a little more out of it before you get rid of it, i'd use this
http://www.barsproducts.com/product.cfm?id=41, some stop leaks can stop up small passages in the system. The other solution is to actually fix it the right way..... BUT you could put the stop leak in it, and trade it in or sell it.
And yes, coolant in the oil will harm the engines bearings, its not a very good lubricant, it'll eat at the bearings, mix with the oil and sludge up.