remove and reinsert sunroof rubber

[ktlimq]

W124.
1992 300D.

On the ceiling, there is black rubber surrounding the hole for sunroof.
(When the sunroof is closed, the rubber is in between the fixed ceiling and the moving sunroof door. You can see this from outside.)

At one spot on the fixed ceiling, there is rust spot right next to this rubber.

I am thinking of removing this rust or applying POR-15 on the rust.

To do this, I need to remove the rubber and then reinsert it.
I am not sure whether the reinserted rubber will attach tightly to the ceiling. If not, water tend to stay in the gap in between the rubber and ceiling, and new rust will develop.

Any advice?