Like they said above, Buck use to have its name on a marlinspike style folding knife. They are not made by Buck currently, at the time they weren't made by Buck either. They were a near copy of a Camillus Marlinspike knife with Buck scales, shield and bolsters. BUT, they carried Bucks lifetime warranty. They currently are priced like collectors items, unless you run across one at a flea market or garage sale. I don't have direct knowledge but I will bet a quarter that if you send one in with a broken blade for warranty replacement you will only be offered a new knife of another type.
Since it sounds like you use a knife with a marlinspike frequently I would go to that big auction site on the Bay and search Yachtsman knives. A Buck will appear as will its brothers from the past. You might also try Smokey Mountain Knife Works online store to get some idea of the value the Bucks are worth if you find one flea marketing..
Some of the fancy salt water sailing Marlinspike knives are resistant to salt water but command a high price. 300Bucks