I source-to-source translated my Modula-2 sources into C code using the mtc tool of the cocktail toolbox (on https://github.com/cocolab8/cocktail-src). This worked fine and since then I maintain the resulting C programs and no longer the modula-2 code. Some editing of the generated C code was done to improve readability and maintainability e.g. insertions and adaptations of the original comments.

This solves all 3 points of the question, since 1) no modula programmers are needed any more to maintain the resulting C code, 2) porting of the C-Code to new hardware is well understood and 3) the tools mentioned for C can be used.

I also have clients who maintain the modula-2 code and translate it to C after each change. With this scheme also newer hardware can be addressed and tools be used on the generated C code.