5900 Remote - keys must be pressed hard to work

[officework13]

hi
i have a 5900 receiver and just bought a remote of ebay, was used and so i took my chances. it works, however, when i try to use any of the buttons i must press them very hard for the remote to do anything. the guy i bought it from said he would take it back, refund/exchange etc, but he said i may wish to try cleaning the contacts. btw, this is applicable for every button, not just the common ones.
so i have a few questions.
is the remote just wore out.
does anyone know what may be causing this and what the fix is.
if i am to take the remote apart, could someone point me in the direction of taking the remote apart.
should i bother with trying to fix it or just send it back and ask for my money/replacement.
thanks