Hello Hans ,

Unfortunately I can't give you a solution, sorry

I own a S3 Wilk and if i remember right you have to pull down the lampshade carefully but with some kind of power , in my caravan it is fitted with three springs

I went now to the caravan to find out whether i am right: In my caravan the lampshade is divided in two parts, a wooden ring and the glass in the middle.
Try to pull down the ring by holding the glas with the other hand so that it can not fall down. The three springs are made of a metal band.
To reassemble the unit i had to put the glass to the roof first and then assemble the ring by moving the glass some mm in its position. You will find a position where it gives a little click and it is fixed.
Hope this helped...