Was the console ever overheated before?
Hmm, I guess not... at least no game froze until now and it didn't smell
burnt if you mean that.

Was it ever operated in an enclosed space with little ventilation that is
allowed to heat up?
Well, it stood vertical beneath my TV... the lower side touched the
board of the shelf but I guess this shouldn't be a problem - would I
operate it horizontally, it would stand on this side all the time.
I remember that sometimes the exhaust fan did spin faster than when I
just switched the console on after I was playing for several hours...

Does the rear exhaust fan work?
Yes.

Bye,
Chris