sunroof sag

Sorry, I never had a car with sunroof so no previous experience. However, it looks to me that your sunroof needs adjustment. That procedure is thoroughly explained in section 77.51 of the workshop manual, pages 3.1/1 and following and it's too detailed to explain here. It doesn't look at all difficult to me but you will need to either source or fabricate two "centering pins", whose measures are including in the manaul as well.

I believe the seal to be part number A 140 780 00 98, but don't take my word for granted, cause this is not the only one in the sun roof mechanism. Part costs € 57.43 in Germany plus VAT so you can count on good £ 40 + VAT over here.

The good news is that the sunroof is not specific of the G, being all parts shared with other Mercedes models. Therefore any reputable Mercedes specialist should be able to deal with the problem should you not want to try it yourself.

before doing something expensive can I suggest a liberal smearing of vaseline around the perimiter of the sunroof particularly around the corner where it sticks,rog