WTF??? If the memory was compromised due to the April 4th fire and water damage event, the whole motherboard will also be compromised. It smells like they cant diagnose the failure so are 'shotgunning' it with unnecessary parts replacement. Be glad its their box you are renting!
OTOH, refitting heatsinks with fresh thermal paste is the proper thing to do if there is any possibility that a system has been handled roughly enough to disturb them.