These have been leaking since forever.
As a Ford tech I can't say much about your dealership phobia. Aside from popping in to Universal's parts department while on training in Calgary I don't have any experience with YYC dealers and I can't point you in any specific direction. All the same, this repair will be old hat for a good Ford tech.
The repair itself is easy but tricky. After dropping the pan you'll see a white and black plastic tab at the rear of the valve body. Pull it down. With the connector off rotate the bulkhead connector counterclockwise and the piece will come out. The old part will have the old style orange o-rings and your replacement should have the black o-rings. Lube the o-rings with Mercon LV and reinstall.
The new piece has to be in all the way in order for the locking tab to re-engage. Sometimes this is hard. Do not force the locking tab - it's only plastic. Break this and you're buying a new valve body. $$$$$$
This is a great time to replace the tranny filter, too.
Install the pan. The filling of these things is a pain. Put in ~5 liters and fire up the truck. Let it get super hot. With your foot on the brake quickly run the shifter through all gears. Go back underneath and continue adding until the fluid level is in spec.
2003 GMC Sierra 3500 -- dually, 4x4, hasn't blown up yet and that's what i look for in a truck
Ford Doctor -- They come in broken and leave fixed. Ford of Canada Master Tech