Cant help you much, but regarding central locking, I had an issue on the 328i, was related to a third party alarm, ripped the thing out and all was good.

These a relatively simple machines (I know its a serious pain with an electrical issue!) but your best bet is grabbing a multimeter and working your way back to the fuse box. Wires may look good visually but you'd be surprised what can happen internally due to flexing/corrosion. It will give you an indication of where the fault lies (may be a module, but you'll spot that too) and you can rerun the faulty wire.

As you think its a module do the issues share a commonality (been a fair few years since I was at an e36) or is there a central location that would logically cause these issues, ie fuse etc.s

Not much help, just my 2c.