Volvo Repair: 1999 Volvo XC 70 AWD, volvo xc 70, three doors

Question
I have had the car since new and have kept good care of it (including all scheduled maintenance) but am having a problem with the electric door locking mechanism on three doors (front driver left, rear left and tail). The front left and rear left will lock when the lock button or remote is pressed but will not unlock without doing so manually. The rear will not lock or unlock except manually.

Can you give me some pointers on how to fix? I would love to have a detailed breakdown on step by step for removing door panels and refurbishing/replacing servo for lock mechanisms.

Thank you in advance for your help!

Answer
Neil, cant do the step by step.  Too long to type.  I havent seen 3 of the lock assemblies go bad at the same time but anything is possible.  New assemblies are best because of the labor involved.  I cant explain how to do some of the steps because its a feel thing.  Roger