Greetings, Werner.

I have tried aptitude and it gives the same result I get with
Synaptic, apt-get or Install Components on trying to bring in
ttf-mscorefonts-installer. That is, aptitude also wants deforma
and x-ttcidfont.conf to be installed as a pre-condition to proceed.

Synaptic doesn't act on requests to install either.

It is apparent that deforma will remove a host of fonts already
installed. That doesn't seem right.

Are deforma and/or x-ttcidfont.conf part of your mscorefonts installation?