Rear passenger seat locking problem?

I have an 02 plate vauxhall vectra 1.8 petrol which failed it's MOT today due to the rear passenger seat (the 60 from the 60/40 split) not locking in its upright position. Basically, the release button was locked down in the open position and the seat won't stay in place. i was advised to bung a load of WD40 in it and see if that would help but while i've managed to get it working a little, it's still not staying flush. i can pull it forward maybe an inch or so before it stops. Any help on this would be much appreciated, cheers