500 bucks for new o-rings?? WOW, I don't see how the o-ring could go bad unless it's made out of poop!! The o-rings don't move around therefore they really shouldn't wear. Doing an entire injector swap shouldn't even be close to 500 in labor. First time I did mine it took 5hrs, second time it took 3. 5hrs. The o-rings don't look like they should be 50 bucks each, more like 3 to 5 dollars per. Dealers charging way too much for things that should be covered are the reason so many of their customers hide fueling boxes and other mods. I say more power to pulling fast ones on the dealer, they pull 'em on us at every opportunity.
Find a good non-dealer diesel shop near you and see what they will charge. You might also check to see if the injector hold down bolts are even tight. Could be that is the only problem. Let us know how it goes.