After taking out the windows, I pulled them apart and cleaned up the frames. They were covered in caked mud and dirt as well as spider webs. And then there was the remnants of the mastic – the horrible black sticky stuff that was used to create a waterproof seal between the frames and the bus. It took a long time to get all the old mastic off but I eventually got it done. I found the easiest way was to scrape off as much of the bulk of it as I could first with a paint scraper, and then use a piece of duct tape to remove the rest.
Once the mastic was removed, I then washed the frames, as well as the walls of the bus where the windows were.
Thankfully, there were only a few tiny patches of rust starting, so I painted the edges with Penetrol to prevent any more.
The bus before washing:
And after cleaning: