Yes, I suppose it's worth swapping the 1GM to eliminate that.
D2026 is the usual error produced for a mismatched 1GM board during bootup
The fault is more likely to be the actual 1KB/1RB though.
Maybe worth inspecting the battery, but I doubt this to be the root cause.
Electronic components do not have infinite life and often can fail.
You have an old system possibly >10 years so electronic 'parkinsons/alzheimers' can set in.
Capacitors drift/transistors internal gains start to drift and not until you power cycle, do these symptoms reveal themselves.
TV's, PC's, washing machines.....anything can suddenly stop working for no other reason but component failure....it happens.