I am having a weird issue with my rear wiper and am hoping someone can help me. When I bought the XJ (1999 Classic model) in the summer, the rear wiper was fine, moved along its path strong with no hesitation

Once the fall hit, around Early October, I began to notice a weird phenomenon: I have to hit the rear wiper switch twice, to get it going. The first push moves it maybe an inch if at all. I then flick it off, and then on again, and the wiper will creep along and develop speed and finally go all the way to the end of the travel path, and back to resting position.

Sometimes I can get away with hitting only once (the switch) after that, but only if it's a really wet rear window. Otherwise it's always a 2-hit operation. Flick switch once. Flick again.

What on Earth is causing this? I tried lubing/penetrating oil the moving areas, but I don't know - bushing? Motor? (The motor looked solid and good last I had my tailgate trim off, but who knows internally).

Of course, with my luck, the one XJ at the local scrappers was donated without the tailgate guts (no wiper motor or arm, or anything )

Has anyone else ever had this? A hesitant but still working rear wiper?