In my experience, the dealer is telling tales. They don't want to do the re-work because they won't get paid a second time.
But, contact Wildwood/Forest River. Have proof that you raised the issue and that the dealer attempted a fix. They'll cover it under warranty and may very likely will let you go somewhere else.
I had a similar issue- the screws would tighten when extending the slide and would back out retracting the slide. The RV repair shop (note, not dealer) basically went through the wall and attached something on the inside. I can try to grab pictures if it would help.
As for who to have do the work, this dealer has already seemingly proved themselves incompetent. Can you find an independent repair shop to do the work? Wildwood will have a process for you to follow for it.