Glo HD freezing - NOT sd card issue

[RoGuE_StreaK]

G'day all
I upgraded from an original Touch to a 2nd-hand Glo HD a while ago and love it, so I eventually tracked another one down for my wife, who's still using her Touch but the battery is going. It sat in the cupboard for a year before she's now relented and tried it. Unfortunately it's freezing all. the. time! Needless to say she's not happy, and I can't return it due to how long ago I bought it (2nd hand).

The freezing behavior is a bit hard to track down; it typically seems to go OK for a minute or so of reading, then become unresponsive to touch. Most of the time a tap of the power button will put it straight into Sleep mode and another tap will wake it and it works for a while, other times even the power button doesn't seem to work, others it acts like it's banked up all touches and suddenly does the sum of the ones received when frozen.

Today I ran some tests by swapping out the sd from mine into her device, and vice versa. Her sd/profile/library ran perfectly fine on my device, no freezing or glitching whatsoever, whereas my sd/profile/library, which has been bulletproof on my Glo HD, suddenly displayed the same killer freezing. Swapped sd cards back again and the same thing, her device still freezes with a card that was shown to be working on mine.

Any thoughts, troubleshooting, electronics repair beyond the typical "new sd card" advice? It definitely appears to be outside of sd card hardware/OS, but the fact that it sometimes works for a period of time and other times doesn't has me baffled. I do have a hot air rework station if there are semi-known hardware issues to track down.

Regards, Lee