For that kind of $$$$ you could have those rebuilt completely by Traxion... and have a superior suspension forever...
I have to call shenanigans and b/s on this dealer, they are taking you to the cleaners on this...
As other have, and may still note, this occurance is not common, and frankly we haven't seen a solitary post on either forum of "worn out" forks... a leaky seal occasionally, but never a worn fork.. coupled with the afforementioned "bad head bearing" which you had replaced shortly before they said yours was reportedly "bad " by them, id find a different service center to deal with...
I'm not saying that there may be a scratch on the tube, or something that caused the leak, but I've re polished forks many times, and re assembled them without issue to stop a bad seal from repeating itself... and it would take a seriously bent tube, one that is visibly bent, to cause leakage..
As for "sliders" or bushings, I don't think these forks have those, looking at the FSM as I have not pulled mine apart yet, it doesn't appear that would be the issue...
Id be seeking alternatives rapidly, and get those forks back, show up unannounced a.s.a.p., and grab them out of their hands, so they don't intentionally "damage" them in order to prove their diagnosis...
Its a shame, I hate this kind of dealer activity...