how to clean the case window

Solution
I have never seen/tried any way of cleaning those acrylic windows without producing scratches. At best, they're hairline and barely noticeable, but they're still there.

You can try using a lint-free cloth, and very gently wiping parts you want to clean. Minimal contact is key here.
Mildly moist rag with a few drops of dish washing liquid should do the trick. Nothing that'll be nasty corrosive.

Windex should do it too. That is what I use.


Or just polish away with a regular rag if you don't want to risk anything. But use some microfiber rag to avoid scratches.
 
I have never seen/tried any way of cleaning those acrylic windows without producing scratches. At best, they're hairline and barely noticeable, but they're still there.

You can try using a lint-free cloth, and very gently wiping parts you want to clean. Minimal contact is key here.
 
Solution
Another way would be to wash the entire side panel with a shower head (the high pressure should clean away fingerprints) and blow dry it for several minutes to make sure there's absolutely no water left on it.

Alternatively you can replace it with a piece of tempered glass (plenty of tutorials on how to do this) and not have to worry about scratches from using a freaking soft cloth on it.