I've done with both of my cars. Found out the hard way that the yellow mark goes to the FRONT of the car.
Buy a jar of vaseline. Clean the old gasket out of the roof channelling. Use COPIOUS vaseline on the new gasket, rubbing it over the new gasket and you can even put some in the roof channelling. Lay the new gasket in place on the roof. Squeeze the new gasket with your fingers and push it into the channelling, working your way around until you're done. The gasket will seem to be too long, but the vaseline will help it slip into place in and around the channel. In addition, the vaseline will prevent the gasket from drying out. I DID NOT use sealant because the vaseline softened and expanded the gasket - I gave the hose test and it sealed tight w/o sealant ! The vaseline is easy to clean up and lets the gasket and sunroof settle. Personally, I'd avoid sealant if possible.
[This message has been edited by PaulJK (edited 06-05-2003).]