Have you not asked this on another string?
How are you with dismantling the machine?
Cos that is what you will have to do.
Under the keys there is a vynil membrane with carbno caontacts- this needs a wipe over and the board under neath will need a clean.
If are dreading the though
Buy a copy of MicroMart rom the news agent- comes ot week ly on Thursday - :ots of repair shop ads ther also spares ads.
Stand by to cancel Christmas though it aint cheap.