It might actually outlast your Model M. The membranes on the Model M seems to be the thing that has died for me (after like 20+ years mind you). I frequently still use my Leopold from 2009 and its rock solid.
Is that an IBM Model M, or a Lexmark Model M? Earlier Model Ms were entirely mechanical, later ones made by Lexmark used the buckling-spring-over-membrane design.
And in the case of a membrane Model M, I wonder if you can get a replacement from...whatever that company is that bought the molds and still makes them to this day.
Sorry to dig up this old reply, just saw it. The original Model Ms were also buckling spring over membrane, you're thinking of the Model F. And yes, you can get replacement membranes from Unicomp for older Model Ms.