I was having major graphical glitches due to temperature - I don't know why some old machines behave in this way (the capacitors on my A1200 all seem to be tantalum not electrolytic - so that rules dry caps out). I fitted (aka bodged) an old PSU fan (blowing air out through the vent) on my untowered A1200 and it's been 100% stable since.
A lot of these old machines seem to display weird heat related issues
