Ok, first things first - WW motor is bad - A stupid piece of soft metal in the gear has worn out and it wont return to the park position. Not a bad job, did Grand Marque in about an hour, aftermarket part was $80 if I remember.
Belts - on my 5.0 Liter never an issue but the 4.6 on the Marque went through 6-7 over a year period- a/c clutch was going bad and would lock up at first it was just a busted belt then suddenly (lots of screeching noise) then either I was fast enough to t/off the a/c or pop would go the belt. It took 3 clutches to finally get a good one, Ford had an issue I guess with the local Reman as they always replaced the part for free no questions asked.
2nd time around it was a bad belt tensioner, actually came loose and would get the belt off center and rub some - not much but I would see the belt wearing and replace the belt, it was not loose by much but just enough to shift the belt to rub on the edge.
Hope this helps. The shop manual will help on the WW motor replacement.