You’re referring to the discoloring/staining on that white glazing strip that holds the glass in the frame? I don’t know if I’d worry about cleaning it, instead, I’d just replace it with new rubber. Also, then you won’t have to worry about it developing any new leaks any time soon either… You’ll probably need to pull an end out to find a replacement, but it will be something like this: https://www.rvpartscenter.com/shop-by-categories/list4/moldings-rv-body-parts/moldings-incerts-seals/window-seals/hehr-1-8-glazing-bead,-10-foot,-black-exterior-window-seal-1810bgb-5490-detail
I believe you need to remove the window from the RV to replace it properly, but honestly I’m in the “preparing to do the same thing” phase, as that glazing trim has started pulling out of the corners on one of my windows in the last week or two.
I tried magic eraser. Mold removal. Nothing removes this.
Source: How do I clean this? It’s on the all of the windows.
