As I believe that my wheelwell problem is unique I wasn't going to post my wheelwell repair. It appears from the correctly installed and captive right (passenger) side wheelwell that the fenderwell plastic flange could not drop out of proper position. I suspect that my fenderwell was never properly installed at the factory. Their answer of a few extra screws and more sealant probably worked for a time. It was not a proper answer to the problem.
After some further thought I decided to post my findings and solution on the off chance that somehow the fender flange can drop out of place and allow the fenderwell to sag.
I found that my left (driver) side plastic wheelwell was sagged down. There was a very large gap where mice and road dirt could enter. I have included some pictures which should help with my description.
On the passenger side the fenderwell plastic flange is set above the frame tab and captured between the tab and floor. It looks unlikely that it could distort enough to come out. On my passenger side the fenderwell flange was not captured between the tab and floor. The fenderwell sagged out of position.
I used penetrating oil (Kroil) for about a week before trying to remove the tab carriage bolt nuts. My plan was to jack the wheelwell up into position and then hold it in place with square plates or washers on the OEM frame stud. As would be expected, the carriage bolt head didn't hold so I needed to use an alternate method.
The front stud was long enough to chase with a die and just add the plate with another nut. The rear stud was too short. Long story short, I added a plate to the front stud and used a slotted washer to drive between the rear nut and bracket to hold the flange in place. I was worried that the slot washer might back off so I added a Unitstrut angle bracket for support.
I find that Unistrut parts are very strong and very adaptable to many repairs. Some selection examples can be found here:
Anyway, it may be worth inspecting your wheelwells on the off chance that they can dislodge from their proper position above the frame tab. It's an unlikely thing to happen, but who knows?
Some pics are attached. vic
P.S. - I apologize for my photography. The fuzzy pics make it clear to see my lack of talent.