Printer Maint. / Problem Question ?

Hello:

Have an old Epson Stylus C40 UX printer, that stopped working.
Red maint. and green power lights keep blinking.

It was suggested to me that the reason was probably that the printer
determioned that
the felt pads that collect excess toner have filled up and need replacement
(or just buy a new printer).

Opened the case up, and yup, the felt pads were totally saturated.

Was wondering how the printer determines this.
Is there a photocell that monitors the buildup ?
Or,... ?

Really curious, as I can't think of a good scheme as to how it would be
done.

BTW: might as well also ask: anyone know of a good solvent to use in
cleaning the outside case
of some toner stains ?

Thanks,
B.