Renew the seal then.
I smeared a little petroleum jelly on the seal to help it a little bit.
It may well be the case that it ages the seal a bit but I wouldn't object to changing it every 5 years or so since taking the sunroof out is a nice easy job if a little fiddly.
I am just doing mine at the moment and am using Silicone grease rather than Vaseline because it does not rot the rubber. Good stuff to have around for things like "O" rings...
