Volkswagen Passat rear passenger door wont unlock

About 8 moths ago i had an engine management light come on and the mechanic at the garage said i needed to replace the wiring loom at a cost of £250.00. Since having this done i noticed that the rear screen wash wasn't cleaning the window because all the wash fluid was going into my boot, this turned out to be the pipe not fitted correctly which i fixed myself. However i then started to get intermitant problems with the door unlocking on the rear passenger door. Now the door has locked and i can't get in unlocked either with the fob or manually. I took the car to my local garage for a service and asked them to look at this problem at the same time, but the mechanics can't get the door unlocked either. The mechanic says the lock must be broken and it will need to be replaced at a cost of around £260.00. In addition to this over the last few weeks i have now started getting problems with my nearside indicator light coming when i lock the car and the only way to get this to go off is to keep pressing the key fob to repeatedly lock the car. Now over the last week i now have started to get strainge displays on my radio, insted of the normal HEART, Raadio 1 etc i am getting TIM 08 displayed.
My MOT is now due at the end of this week so i need to get the rear passenger door unlocked or it won't pass, but I don't think the lock is broken either. I think this is an electrical fault which has stemmed from the wiring loom change and the screen wash pipe leaking into the boot due to incorrect fitting. However i can't seem to get this across to the mechanics at my local garage and they just want to change the lock. Can anyone offer any advise on alternative solution or where i could go to get the electrics checked at a sensible cost please? VW wont to charge £85 - 90 to hook the car up to their compluter and this is before they will even look at the problem.