My left hand shift key does not work ...

... on some letters: p,o,i,u,y. it seems very odd. i have taken shift key cover off and cleaned it. the shift key works on other letters, such as R, without any problem.

So this is typing the top line of letters with the left shift on:

QWERtyuiop{

and with the right shift:

QWERTYUIOP{

is this a fault of the keyboard or something that can be fixed?

the keyboard is an old eMac one, but has been fine.

thanks, p