Hi Dave,
LCD displays are sensitive to moisture and are hygroscopic.
Moisture will eventually destroy them.
I too have a multimeter from my early days.... My first DMM has the same problem.
I bought this multimeter in August 1980. The display needs to be replaced to ensure future use.
I too am left wondering if I can find another such display.
Greetings from Holland. Holland in Europe. (Not Holland in the USA)