AnthonyL brought next idea :
He can't find the instructions though it doesn't seem that hard to
operate, but there is a low battery warning. I guess this is
understandable anyway after 10yrs but I can't find any instructions as
to how to replace them, or what regular maintenance is needed eg
lubrication.

Look online for instructions.

They are worthless second hand, though resellers will happily take them
away and resell them. Maintenance is minimum, just a wipe down with an
oily rag. Fit some new batteries, it will be fine. The batteries last
for decades, if looked after and not discharged - basically left
diconnected, but given an occaisional charge. Whilst connected, there
is always some discharge, unless mains power is left on.