GTO rear view mirror replacement

My D8GTO rear view mirror has corrosion coming from the inside, causing irritating visability blind spots. Incredibly annoying. The OEM part number is from a Ford StreetKa. The Ford OEM #number is: 1644638 priced around 70 Euro’s and a second hand on EBay for around 20 Euro. I sprayed the back of the mirror in Fluidfilm via the bottom of the mirror to prevent this from happening again.