It's weird - not talking about the clear bit that works at the push of the button but the sliding part you manually push back first. This only slides about half way (the vent bits aren't showing) then the actualy sunroof opens properly but obviously gets stuck on the sliding part and can't open fully. Not keen on pulling the whole thing apart, any ideas?

Never done ths before (first CLK - dream car) 1997 model - good condition - open to ideas of where to start?