Now then now then. Memory time

I believe the GM's auto box (ar35) was also fitted to some BMW models under the guise of 430L (?) or something along those lines....? And got wondering if they're interchangeable between models? ... And Marques...?
In short are they the same, bar bolt patterns to bell housings and lumps etc.
Reason for asking is, mate has a BMW 3.0d e39 touring, does mega miles in it for his business, and the auto box is going into limp mode on occasion.
This is not the cars original box, it's a recon some 4 years and 120k miles old which cost 1500 sobs. The original did similar miles I believe. Yes it's a high mileage car, but it's absolutely mint.
I suggested that a re con box sounded rather expensive given what we pay for used working boxes on here. £100 not being uncommon afaik? He said used boxes sourced from BMWs go for thousands, 2.5k in some cases. So re on makes sense, except are they the same as omega items?
All sounded like a plan until we realized his is 5 speed and ours only ever got 4 gears in the uk..... could one from the continent work? Without knowing their price over their.
Btw, there are no other codes in the car other than one showing a difference in input and output speed. Which means it's slipping I guess? This being the exact same code when the previous box failed. It is chipped.
Anyway, are these the same boxes or am I barking in the wrong tree?