Hi tech90

I've had this problem before and was told I'd need a new lock. Then a mechanic friend of a friend suggested that dust and crud is the usual culprit so remove the locking section and shake it vigorously whilst immersed (yes immersed) in degreaser solvent. Blow out the residual solvent with an air hose and allow to dry then replace the lock.
If your problem is caused by dirty accuators this will fix it - well at least it fixed mine and 2 years later its still fixed.

worth a thought??

jd