I had never heard the word "fettler" until reading this thread. I am aware of the term "fettle", as in the term "fine fettle", which I guess means everything is copacetic for that individual or that object. Wikipedia has several disparate definitions for fettler, only one of which seems applicable to the care and feeding of an LP12. See definition #3 here. And even that definition does not specify that the thing is done well.
Is fettler a term adopted by Linn explicitly to refer to a tech who is qualified to work on the LP12? If so, an inept fettler does not leave your LP12 in fine fettle.