Take the car elsewhere, it doesn't have to go to Fraud to maintain the warranty, as long as they stamp the book it's valid.
I wouldn't worry about resale value either, it will make no difference to desirability, plus most of the time the dealer get the apprentices to do it anyway which is more worrying having them round the sump plug off.
I was thinking of taking it to the independant Ford garage that did the wiring for my dash cam, they seemed to be pretty good even though they didn't know how a fuse piggyback works lol. I'll get a quote from them anyway to compare.
My local dealer is also the one that did my Mountune upgrade, so they have at least one mechanic who knows what he's doing.