Line capacitors or "line filters" are capacitors connected to the power line. Disregarding all the other capacitors that might be bad in there, a line filter is the most likely thing to be causing the chassis to be hot. In the old days, they just used regular capacitors for this. X and Y capacitors are modern units that are purpose-built to be line filters. This is important because they are still connected to the power cord even if the unit is switched off.
There is a good page on them here:
http://www.justradios.com/safetytips.html
Any old line filters should be replaced even if they are not bad. X and Y caps probably wont fail in this kind of service, and if they do, they probably wont catch fire.
In your case i'll bet there is a capacitor in one of the chassis connected from the power cord to the chassis, and it is bad.
John