Is it worth repairing a 15 y.o. Nikon F90X?
I don't think I've ruined the shutter but I've very very gently rubbed the blades with isopropyl alcohol to clean them. Very gently means letting the microfiber cloth (the one that is used to clean glasses - very very thin) rest on the blades under his own very weight. The blades did bend a very little while rubbing but they returned normal after. I've never touched directly the blades.

Can a shutter be ruined this way?

Is the repair economically feasible?
I can buy a new F75 for something like 180$...