I own a 2006 Tacoma that is
I own a 2006 Tacoma that is going to have the frame replaced. I was told it would be "descaled" then tested for holes. They didn't bother to scale it, they just found a small hole and that was enough.
From what I have been reading online Toyota doesn't "Pay" for the replacement, the dealer is paid, 40 book hours to do the job. It used to be 60. Of course they can do it in under 12 hours with two people so there is profit to be made here. If they were to undercoat it there would be less profit margin.
Dana, the frame manufacturer, has paid Toyota millions and if the dealer wants a piece of the pie they must prove your frame is perforated. a ten mil hole or more.
In the beginning the frame undercoating and the replacements were rough and may not have gone well.
Now there are employee's who do nothing but replacement and undercoating so I would have to guess they are getting better at it. It all seems to depend on your individual dealer if they expect you to pay
anything or nothing at all.
I can only hope that I have as good an experience as other people on this forum.