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Today, while I had company, I made the HUGE mistake of forgetting to remove the thick small table cloth that I use as a dust cover on top of my 62 lb (mention weight so you know it can generate quite a bit of heat) A/V receiver when it is not on.

After watching a movie using the receiver (in stereo, not surround mode) for TWO HOURS with the cloth accidentally sitting right on top of the receiver which has no side or rear vents, the receiver 'overheat' indicator kicked in!
I am amazed it took that long, considering I had the heat on and the fireplace on in that room and that the volume was pretty loud (the video's audio was low quality and it was hard to make out the voices without turning it up).
It was dark in the room, which may explain why I never noticed the cloth (which can only be seen from the top for the most part).
As soon as the indicator light went on, I walked over and immediately realized my mistake.
I was upset at myself for forgetting.
I then went to turn the main power switch to off, so that it wasn't even in standby mode, but accidentally turned it on again (the full power and standby power buttons are one right above the other); within three seconds I hit the full power off button and turned it off completely.
(I guess it is a good sign that it turned back on, meaning that at least it isn't dead).
I also turned the fireplace off.
In order to be extra safe, I am letting the receiver sit (at least) a few more hours before I attempt to turn it on to test it out to see if there was any lasting damage.

Can this overheating due to almost no ventilation whatsoever cause permanent damage to ANY components IF the protection circuitry kicked in, as it did, after over two hours?
I know it probably depends on a number of factors such as the room temperature, how long it was on, how loud the volume setting was and how little ventilation it had (in this case ZERO since the cloth was DIRECTLY on top of the receiver), but any feedback from anyone who has experienced an overheating receiver or knows enough about what extremes the various components inside it can handle, would be appreciated.

Which particular internal components typically overheat?

Never a dull day!

Thanks!

PS: From now on, I will drape the cloth over the front display panel when it is turned off; this way it will be impossible to forget to remove it before using the receiver.

Update:

I just finished running the receiver for about an hour using EVERY component hooked up to it.
Thankfully everything worked flawlessly and it didn't overheat or shut down.

I will have to assume (or hope), for lack of evidence to the contrary, that the various internal components didn't suffer from the overheating and that they will last as long as they otherwise would have.

I am not an expert on diodes, capacitors, transistors and other components and circuitry, so I don't know if the overheating problem I experienced could have led to "wear and tear" of any of the components, despite the fact that it works fine?

PS: I forgot to mention in my OP (Original Post) that the movie was actually stopped for about half an hour, in the middle while we had dinner.
This may explain why it took so long to overheat - the receiver had a chance to cool off somewhat or at least not get hotter, while the film was paused / stopped.