I have no idea what you did, but a shutdown is a shutdown - there's no way a PowerBook would get hot after a shutdown, unless you have a broken battery or the thing... did not really shutdown, but you'd hear the HDD spinning then for instance. Letting your machine run with the lid closed, on the other hand, isn't a good idea in general. The machine can't cool itself easily with the lid closed and MorphOS has no sleep mode whatsoever, so in best case you'll just put a lot of strain on the fans, which are not designed to run 24/7.

Also, $500? Ouch, they're not worth more than $250.