I am trying to clean all the old silicon and unknown adhesive and its a pain. is there a solvent I could use that would dissolve pretty much anything other than the plastic window? i don't know if the window is acrylic or plexi...
There is no commercially available product I know of, and believe me I have searched, that will remove dried silicone from plastic. Silicone is resistant to most chemicals and that is part of why it was developed.
All you can do is rub it off with your thumb then wet sand it after taping off the areas you don't want sanded.
If this is a hatch or portlight Dow 795 is the preferred sealant to re-install.
Acrylic basically is plexi, Lexan is polycarbonate. Unless the PO changed the ports/hatches to polycarb they should be acrylic..