Hour Meter Tough to Read

I have a 1995 345 with an hour meter that's almost impossible to read. The "glass" (or whatever it is that acts like a lens) is a dark amber color and it makes reading the hour meter next to impossible ---- but given exactly the right lighting, it can be read. I don't know why the dark amber color --- I just recently purchased it. It's low hour but almost 20 years old and it has sat outside and covered for most of its life.

Anyone know a way to fix it short of replacing it?? I tried a pocket knife on the extreme outside edge, but the glass fractures and chips easily --- if I keep that up, it will be impossible to read.