The DRAM was always an issue, the 8x2K 4116's in the lower 16K needed 12V and -5V, and those rails going tended to go and take the chips with them. The inductors also buzz quite loudly these days.
The upper 32K was actually 64K, 8x8K 4164 chips which were only half bad. They would be binned so the faults were all in one half or the other and jumpers on the board select which half to use.
Usually though, the Ferranti ULA's burn out long before the RAM goes bad.
The heatsink was missing on the board in Dave's video, it is normally a lump of aluminium bolted to the 7805, but they too get rather hot as they dissipate 5-10W sometimes.
Thanks,
Dave