HP25 suggestion for repair please

[murphy9]

This HP25 is behaving poorly - it's been in a box for 7 years and transported around the world US-> UK -> Australia. The 4 and 5 keys behave erratically, sometimes blinking but not registering a 4 or 5. Tapping 123456789 delivers 123656789 in fix2 mode, in fix8 mode the display registers 123666789 ! This was with new batteries. I've never used a charger.

The logic board has very minor oxidation around the battery terminal, but this doesn't seem to be anywhere else - I've cleaned it with the usual vinegar/ alcohol. Tracks that are visible look ok and none of the pads look like they have dry solder joints.

I've not touched the keypad (nor do I really want to if possible). Any suggestions appreciated for the next stage - worst case I'll put it to the side and wait for the Panamatik kit to become available again.

Thanks in advance Mark