Having owned my 1999 BMW 320d for a while I started to experience central locking faults. THe doors would always lock but would open occasionally and the deadlocking mechanism would kick in when opening the drivers door manually. This was causing difficulty in being able to open the doors and take out the family. I started off by getting a new key from a BMW dealership cost £100. ouch !! Still there remained a fault. Back to the drawing board and a visit to the local dealership for a full diagnostic check at a cost of £40. THe result was a faulty GMU - General Module Unit and an estimated total cost of replacement in the region of £400 ouch !!.
I thanked the technician for his effort and declined booking the car in for the repair thinking there must be a cheaper option. I spoke to lots of people and found that the GMU was coded to my car available from BMW at a RRP of £225. Still cheaper than having a dealership sort out the problem but I was determined to get a cheaper resolution.
After many hours of research I found the answer - purchase the central locking relays and fix it myself. The cost of two relays from the good old USA was £23 inc postage found on Ebay.
I then sourced a local technician well versed in the delicate art of removal of the old damaged relays and re soldering in the new ones. And bingo I now have fully functioning central locking again.
I must say that there is a requirement to have the correct tools and this guy has some Gucci kit which would be essential. No standard off the shelf soldering kit would suffice. The risk of damaging the module is ever present so "don't try this at home" unless you are really confident.
I am not sure if he would do this for anyone else but I could ask if anyone was interested. You would need to obtain the relays remove the unit and send it to him. I would ask him for a price or put you in contact direct.
There are some good guides on the web for the removal of the GMU which is not too difficult takes about 20 minutes. Make sure you disconnect the battery before removal.
I hope this is of some assistance.