Do you smoke? One of the worst machine killers with which we used to deal was nicotine. It tends for form a sticky, non-thermally conductive layer on chips. Over time it also collects dust which increases heat insulation.
And to Cammy's cap recommendation, it should be pretty much standard op these days to replace any electrolytic caps on a vintage board of any machine. One of my TI consoles was acting up due to a bad cap, and I fixed a previously dead 7800 by replacing its capacitors.
