TCU...still one question
 

I want to replace my module (pre bluetooth 2004) with a TCU that will allow me bluetooth operation.
There are many used units on ebay of course but I still have one question. Assuming that the newer units have better software, how new can I go for a 2004 X5? They all appear to be the same physically but is there a point at which a TCU from a newer BMW won't work with my 2004?
Thanks,
Steve