Hmmm IIRMC I was told by Steve at MBenzNL not to leave it partly up or dwn - that stresses the delicate plastic parts.... Anyway mine has been fine since Steve put it in a couple of years ago. And the comment above about German engineering is spot on!i've had intermittent problems with the sunscreen.
when you're screen starts to work again, never have it fully opened or closed. ever notice the non-fully opened sunscreens? there's a reason why. it must be the alignment of the gears.
hope this helps!