I have recently had problems with my Remis Vario 1 roof lights. Very stiff to open and the winding handle clicking when trying to lock. So I decided to get on the roof and take them all to bits, I soon found out that it is the winding handle that needed replacing but what is the cause. The gearbox's were completely void of grease, its quite an easy fix and had I known that these things have grease in the gearbox I would have checked and serviced them before needing to fork out over £40 for two new handles.
The handle is designed to click if there is a problem to try and stop damage to the gearbox but after months of the handle clicking the handles cogs wear that that's game over. So a word of warning if you have these on your MH, get up on the roof and great your gearbox's