How to replace bluetooth module please help!

2008 phaeton 3.0 tdi

I was having a whole load of electrical issues with this car, bluetooth stopped working, then the boot, then the drivers side seat and memory etc.
eventually the battery drained. never had any problems with her so was worried.
got both batteries replaced and something was still causing electrical problems.

gave it to the dealership and they usefully told me that im right the battery's drained and charged me. nice. further diagnostics will cost ££££

gave it to local mechanic, turns out the bluetooth module is the problem and is draining the car batteries
a replacement from VW will cost over £4000!!
the part number is 3W0 035 385 AS that i need

i'm looking for a second hand part but i cant find the exact same one
i have found a bentley one - 3W0 035 385 H - will that work?
or i have found a VW one - 3D0 035 385 A - but i dont know if these are compatible

i also heard not only do you have to have the correct part but it has to have the exact same software on it? is this true?
is there any way around this other than just doing without bluetooth?
is there another module out there that i can retrofit or even upgrade to?

looking forward to your advice!!

managed to find one on ebay for £110! lets hope it works, its arriving soon
3W0 035 385 AS was in my car

but its been superseded by 3W0 035 385 AT for your information. the module is located in the roof of the boot i've been told.

i'm still interested in what my other options would have been - anyone done any bluetooth upgrades out there?