Rust on Rear Side Windows Golf IV

Hello,

I've noticed rust on the triangular supports of the rear side windows of my Golf IV. The black paint is blistering. The adjacent, continuous support is not affected.
I find this very unattractive, and I would like to replace the triangular pieces.
Can someone tell me how much effort it takes to replace these?
It would also be interesting to know if this is a very common problem.
My Golf was manufactured in 1999.

I probably can't claim the 12-year warranty against rust, because a colleague with the same problem was told by VW that the crossmember is not part of the body.

Best regards,

Frank.

"I also have these rust bubbles on my Golf, which is a 1998 model. So far, they haven't burst. I noticed the first signs of it about 3 years ago and reported it to my dealer. He said it wasn't bad enough yet. Now the car is too old to qualify for any warranty coverage."

To replace it, you need to remove the interior door panel and then the metal bracket to which the window regulator is attached (remove the window regulator). This is quite a bit of work, and I don't think it's worth it considering the problem.
If it ever "blooms" properly, the question remains whether it can be fixed with the window open.

I don't know how much the new rails cost.

'Hey, I also have this 'problem' with my Golf IV, I think it's from the year 98.'
It's strange, otherwise it looks like new, except maybe for a little bit of rust on the rear silencer. But these window frames have been rusting for 3 years now...