You could always try and "pop" the keys off the laptop board and see if there is any dust/fluff stopping them working, otherwise you may need to drop the laptop off at a Sony Service Centre to fix. I'm not sure how much that would cost though - I guess it is out of warranty?
As Ian said, pop off the offending keys (you can buy a special tool for this, RS Components, amongst others, can supply one) then vacum out any dirt and fluff.
If that doesn't work a small (read small) squirt of WD40 into top of key, so it penetrates the interior, may work.
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