Central Locking System Problem Help

[The Melmaan]

I have one of the local shops here install an after market alarm system on my E34 last year. It includes a keyless entry system. My locking system only works when the driver is unlocked, all the locks will unlock including the trunk.
What they did was they have installed another actuator on the driver's door to activate the locking system. It worked for a while until late last month. I have tried syncronizing the locks but it now a mess. I took the car back to the shop to find out if the actuator they have installed is not working anymore. They said that the actuator is working well, the line between the lock and the main brain is not working, it could be the central locking system. Could this be possible?
I found an item at Ebay and the item is:
BMW E34 E32 GM General Module Black Box
Is this the unit that need to be replaced? How can I test the unit in my car without going to the dealership?

[shogun]

but you first have to fix all the probs with microswitches or mechanical probs on the locking system.
There was an old GM with some 'features' and a new GM. New GM has the following:

-Repeat and time interlock for headwashers, time interlock 3 min.
-headlight washing pump at fifth windshield washing after time interlock
-intensiv washing pump operating at reduced time from 3 to 2 seconds
-minimum interval for wipers reduced to 2 from 3 seconds (programmmable)
-increased wiper contact pressure during windshield washing now also provided

-previously the GM would react opposing signals (e.g. an unlock signal while trying to lock, as with a defective microswitch) by carrying out the first command (e.g. locking, followed immediately by unlocking). Repeating the first command then results in carrying out the command, e.g. try to lock again, and locking is now carried out. This function (Asynchronious Position) is omitted in the NEW GM.
-After unlocking is performed due to crash sensor activiation, the locking command is now reactivated by double-locking with the key from either side (driver or passenger door).
-The one-touch operation of windows has been expanded to all 4 windows in opening direction. Drivers side has one touch in both directions
Sunroof is not already in the tilt position.
-switch off delay of the interior lights after entering the vehicle and closing the driver's door reduced from 20 to 15 seconds.

p/n of new GM from 09/91 is 6135 8 356 095 and many others.