Seems like a missed opportunity. Why not fill a built in sponge with that paint instead, and when the sponge is fully saturated it's time to throw out the whole machine and buy another one?
Lets not leave the Service people out, they want to get a bonus this year, too.
So make the sponge replaceable, but only with a field maintenance call-out. The sponge unit will have an NFC chip in it that if it's removed will lock the unit out until a Technician access code is entered to restore the unit.
We can sell it as a whole periodic maintenance thing - give the service guy a can of air-duster and a roll of paper towel to wipe the thing off.
(I feel dirty even writing this because I'm sure someone is taking notes and thinking these are great ideas)
