I was thinking that it would be possible to replace the membrane assembly with actual buttons.
Alternatively I have a special conductive paint that is used specifically for refurbishing rubber membrane type keypads, I use it to repair ageing commander phone systems and it works very well.
I'd be willing to have a go at repairing it for you if you could do without it for a week.
Otherwise, can you replace it with one of these?
http://telescopes.net/store/telescop...and-lx400.html