If the unit is not rusted inside, which would alter fuel delivery, I don't see any reason why you can't open it up and replace the o-rings. I know several people that have done this and they have been pleased with the results. Use acetone to clean all parts, and make sure you don't drop the plunger on the ground. Save your $$$. A rebuilt unit is probably close to $1000.00. Mechanics of yesteryear would fix things rather than replace. Buying a rebuilt unit means buying something that was fixed just enough to last through the warranty. Good luck.