The compressible band between the window and the outer wall is coming loose

With us, the [Kompriband] installed between the window and the outer wall is slowly disintegrating. It is gradually turning gray and crumbly. I already had a professional come by because of this, but he was also at a loss. He said he could apply silicone over it, "although that is no longer done," or alternatively leave it as is and continue to monitor it.

Does anyone here have an idea?

If the expert is at a loss, then in 99.9% of cases he is either the "executor" or not an expert.

If the expert is clueless, then in 99.9% of cases he is either the "performer" or not an expert.

Or some things can no longer be "properly" repaired. If you break the broomstick, the carpenter might be able to glue it, but it still won't be whole.