I have this 'older' (1990s) bike that seems to have developed a "click" in the BB area. So, only "clicks" when pedaling, nothing else down there seems loose (like the cranks).
Do you think I toasted this BB? Is that difficult to replace (model a STX MC-32) ? I can't think what else might be wrong with it.

I has a similar problem with click sounds coming from my bottom bracket last week.

Check out this website for sources and solutions: https://www.jimlangley.net/wrench/keepitquiet.html

I found that my lock rings and pedals were a bit loose. It was as simple as lubing up the lock rings and tightening the heck out of them, and lubing and tightening up the pedals. No more clicks!!....I thought I had a toasted BB too since mine is pretty old. Been riding all week without issues.

I'd suggest making sure everything is lubed and tight before running out to buy a new BB.

The only reliable way to check the BB I've found is to pull the cranks and turn the spindle by hand. Rough, draggy, sloppy.... Best to replace. If the spindle turns smoothly with no up-down or side-side play... Check the fastners as Staylucky says.

Right on, thanks guys, I'll try lubing it tonight ...