In message , The Natural Philosopher
writes

Unless its heavily integrated with e.g. steering column controls, just
rip it out and replace with something better.

OK. Assuming I'm that brave. Current model is Blaupunkt Como RCM 148,
and eBay has the removal tool. Assuming I can get the old radio out,

Is the hole in the dash likely to be standard size?

Are the securing catches likely to be standard?

Is the electrical connection likely to be a standard plug/socket

Or is the whole project likely to be a nightmare?

I guess the first job is to get the removal tool, ensure I can get the
old radio out, and see what is behind it. Car is 1998 Merc C200. I
just worry that the combination of Merc and Blaupunkt means that nothing
will be 'standard'.
--
Graeme