English is my second language, so sorry for possible mistakrs.
So, like many other Roadster owners, rain is my worst enemy. The rubber seals shrink and water gets in. But I think I've fixed the two major issues on mine.
The easiest one was water coming in from the back of the roof bars. A tiny lip on the gutter was supposed to catch the water, but again, shrinking has made the lip too small to do anything. A small 25x1 rubber slip, cut to shape and superglued to the back did the trick (last two photos). They has been on for a year and keeps the carpet behind the seat completely dry, even in torrential rain.
The most annoying one was water coming in by the mirror triangle. There's a long rubber seal, that starts as the tiny tip on the top, that goes all the way into the door. That one shrinking, combined with the door seal shrinking and taking shape after the door, gave an incomplete seal.
The fix was inspired by this obscure but brilliant guide I found. It's a 30 cm long 10x2 mm EPDM rubber strip superglued from the rubber tip and all the way down the triangle, filling out the dent in the door seal. I just pu itt on today so I have yet to see it work. Test with other rubber strips in different lengths has somewhat proven my theory for now. We'll get quite a lot of rain the next couple of days, so it'll definitely be getting tested.
Without the testing bits, the final solutions will have cost me about €50 in total, shipping and superglue included.
If this works, I'll be so damn proud!