That happened to me, so I welded it and it was fine for a while. However, on mine the felt "groove" in it was missing, so the window rattled especially when shutting the door. A very helpful fellow forum member was breaking a car so he kindly sent me a replacement that had a good felt insert, and it's now great.
I reckon your options are a good second hand one or a bit of delicate welding to the one you've got (remove the felt first of course!).
At least V70 and 850 are the same door, so you've got decent scope for getting another one.
Cheers
