Welcome to the mad house.
Wojtek has about covered the window problem.
These windows are, from memory, fitted from the inside, so it's possible to mask the outside of the window, then fit it in place, add a small drop of liquid cement and let it run around the recess of the 'frame', and allow to set.
Then, apply the Testor's stuff around the edges of the outside, using a sharpened cocktail stick, wiping off any excess with a wet finger tip or damp 'Q-Tip. This will seal the rim of the window, and reinforce the joint. Further applications can be made once the 'glue' has set, filling the surrounding gap and making the window flush. This area can be painted after it's set, giving a flush, 'fitted' look to the window.
I haven't seen or used the Testor's product, but I'm guessing it's similar to Humbrol Clear Fix. I use the latter, and also plain PVA (white glue), which is basically what the 'window kits' are made of.
Regarding the damaged part, Revell have a service on their web site for ordering parts, free of charge. You'll need the kit number and name, and the part number and description of the problem - it wasn't damaged by cleaning with thinners, it was broken or deformed on the sprue !!