I've got the same issue. It appears that either the glass drops slightly over time, or was originally fitted marginally too low in some cars (you can visually see a difference in the glass alignment between cars), this alignment then traps water.
The bodyshops I've contacted (so far) don't seem interested in anything other than insurance work. I bought a replacement from a breaker, it's slightly better but not perfect.
Depending on the age of your car, it may be worth checking if Renault will cover the repair/replacement under the 12 year anti-corrosion warrantee.
Best of luck.