I agree with MrCjames - sorry but me no have 3rd brake light so never thought of that. He is bang on with the spring clip marlarkey too!!
I have had wiper motor out - it had seized, water had penetrated down the shaft and done the damage - I got offered one from a breakers at a good price so fitted that. The seized unit is with a friend - he pleaded with me for the opportunity to have a go at restoring it - hell you cannot break something twice!
I suppose best policy is to exercise the tail gate wiper regularly, say weekly, that should prevent seizure.
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K