[boxster_nut]

The door lock mechanism intermittently does not lock.
1) Sometimes, pushing the button on the key fob locks the doors, flashes parking lights - all OK
2) Sometimes pressing the lock button on the key fob causes the locks to close, flashes parking lights, then the locks pop open, horn beeps
3) when 2 occurs, inserting the key into the drivers side door lock and turning the key quickly 2 times
*sometimes* locks the doors and *sometimes* not.

I am looking for some advice on where to start looking and some things to try to fix the problem. Is there a sticky on this site the provides some guidance? - have not been able to locate it.
I came across some postings in the forum that talk about replacing the door locks with volkswagon p/n...how can I determine what door is causing the issue?
TIA
j