Fixing siezed rear wiper mechanism on 2nd gen and up.
Moisture seeps through the "O" ring on the shaft between the arm and housing on 2nd gen rear wiper mechanism.
White metal housing that wiper shaft goes through swells up with
corrosion, seizing the shaft. Ford probably didn't put adequate lubrication from new. Bronze bushing is usually OK. Remove "C" clip to take mechanism apart after removing wiper arm shaft nut and two nuts holding mechanism to glued in plate on rear hatch glass.
After removing corrosion from shaft housing I pack in a water resistant red grease containing silicone that is used for the sliding pins on brake calipers. It's called "Siliglide". For good measure, the "O" ring, if not damaged, gets the grease and extra "O" rings are added OUTSIDE the big nut before the wiper arm is attached.
They're not going anywhere and will help keep moisture out of the
housing. A bad execution of the rear wiper design by Ford, IMHO. The
1rst gen rear wiper was more complicated and expensive to
manufacture, but for me, was more reliable than this one. Haven't had
any issues since rebuilding mine. Occasional usage will probably keep it from siezing again. With this design, I think not using it may allow it to freeze up faster. Do it to yours instead of wasting over $80 on a new mechanism.