Sunroof

They have drains on all four corners the fronts go thru the "a" pillar and exit behind the panel on the front fender, the rears thru the rear pillars thru the trunk and out near the air flap behind the bumper.
If the gasket is bad it is available and can be replaced $150, it is a litle tricky but patience will get it in. I would look carefully at the old one because it has two different lips and there is a up and down. I had a rust spot taken out in the corner, and opted to relace it rather than mask around it. The idiots ( non MB body shop) stuffed it in by starting it and then working around the opening it was then too long and they cut it. The roof would not work properly. I made them buy another from MB and installed it myself, corners first, and then work it in all the way. I used a small wallpaper roller to seat it. "perfect" I have not cleaned the drains or had any problems.

You may want to first put some vaseline or better yet, a purpose-made silicone rubber spray - just to freshen up those tired rubber seals. Mercedes UK use the one you can get at your local Halfords, can't remember the name but definitely begins with an "H". Also good for your window frame seals - makes windows go up much smoother (and makes it easier for your mechanisms and motors as well thus prolonging their usefulness). Spray on door seals too to make them more pliable and soft thus preventing damage during winter months.

Thanks posix for that info.. will be of to the big H tomorrow..
Thanks also to you peter for your input..well informed as always..

Just remembered, if you have a BMW dealer local to you they should have an item called "Gummipflege" (rubber care). It's basically the best rubber seal cream there is and detailists and concours people (and I) swear by it. It comes in a green tube, costs about a fiver. When you take the cap off there's a spongy applicator - just squeeze a bit and rub on your door, sunroof and boot seals.

Oh and also in case you want to clean your windows - porsche makes the best window spray.

P.S. and it seems that mercedes has introduced the best leather cream by using meguiars as their supplier. no shiny stuff just pure matt.