Markus do not worry as I ask myself the same questions.
From what I've heard there is no hope one can solden anything over Zimmerit. The Germans used blow torches to dry up the mixture and the reputation of beeing inflamable comes from Zimmerit not being properly dried and still with solvants in it.
See what I mean ?
I confess the StuPa is a mistery to me but I'm not sure (understatement !) this Zimmerit is original and as you can see on the pic the brackets are just "put there" fixed with the same "plaster" or "putty" or whatever they used to simulate Zimmerit. Anyway they are unable at that point to fix the track links on the glacis as you can see from the picture. Only one end (left of the picture) is properly connected.