I smear some Vaseline on the rubber seal. Seems to stop it!
When I went to Boots to get a big tub for this purpose I couldn't find it so I asked an assistant. She said "is it for lips or for baby?" I said sunroof. She just looked puzzled!
Nothing lasts, they are basically the crappiest sunroof on the planet
I have now got mine sealed shut with sikaflex, no more leaks, but still condensation drips on you!
vasaline (other petroleum jelly products are avaliable) worked well for mine.
I took the glass out completely, washed it and applied all round, been good for 17 months so far, and yes I used it in the summer too