I have just opened a troublesome Guruplug which had been losing its HWclock frequently and lo, I beheld an extremely swollen LR1130 button cell battery. On removal, I can see there is corrosion on the battery and some on the tracks. Hopefully I can clean and seal the tracks and replace the cell easily. The Guruplugs have been in service for about 2 years and the temperatures have probably accelerated failure.
I will watch the future performance with interest - especially if i/o errors are resolved due to bad time stamps.
I am going to institute a general battery replacement program at the next kernel upgrade.