MEK is nasty stuff. Back in my 10 pin bowling days (early 70's) it was used to soak 10 pin bowling balls to soften them for better traction and less 'slide'.
I would think it would melt a plastic window very quickly. Stick with polishes like brasso.
Mine was similar after very low miles over the covid lock down.
There was some loss of fluid and some dampness around the slave cylinder.
The pedal was right down on the floor. Some pumping the pedal helped, but very short term.
A new slave cylinder helped, but there was some sticking of the pedal and not returning to 'full up'.
After using daily for a few days it returned to full pedal again.
I assume that the clutch shaft was being a bit sticky until being used again.