[X1F48]

Hi all,
I couldn't find a post related to this, so I had to open a new thread.

My 2015 X1 F48 recently had transmission issues, where it would enter reverse gear with a sever jerk. After a while, I completely lost forward movement in the car. Only reverse gear engages now.

Car is at 61000km, gearbox oil never changed. I bought this car used, at about 40,000km a couple of years ago.

The computer threw a few warnings:
Gear ratio monitoring, gear 3: c1 or c3 open incorrectly.

Speed sensors: transmission input speed and engine speed in R implausibility.

Apart from these transmission warnings, I also have the oil pressure switch warnings:
Oil pressure switch 1: short circuit to B+ or open circuit
Oil pressure switch 5: short circuit to B+ or open circuit



Draining the gearbox oil, it looked somewhat murky. Like a dark brown.
So we flushed it with Liqui Molly transmission flush and refilled with recommended oil.
Still no change in the issues we had (we did the flush just suspecting the oil was too old and had thickened out).

So we took out the transmission, and while doing so, we noticed that the brand new oil, which was light red, had instantly turned murky, dark brown as well. How?!

Opening up the transmission, we have no clue how, but there seems to be rust build up inside? How could this happen?
Please see attached images.

We could try rebuilding the valve body, but the mechanic suggested we replace the entire gearbox due to the build up of rust. He suspects it could start building up once again, if we just rebuild it.
Note; the repair is being done by a personally known mechanic friend of mine, and not at the BMW agents, as those guys are ridiculously expensive over here in SL.

I've been looking for the exact gearbox to replace mine but have not been successful.
Transmission model: Ga6f21aw

I have two questions:
1. Will rebuilding the existing gearbox be fine? Any idea how corrosion has built up? Has anyone experienced this before?


2. If I decide to replace the whole transmission, is it possible to switch it with any GA6F21AW gearboxes OR does it need to be the exact part number?
Is there a way to use, say, a mini gearbox by swapping some components?
I haven't been able to find a single used gearbox with the exact part number of mine.
Brand new is available at over 4,000 euros.
However, good, used Mini gearboxes with same model GA6F21AW is available on eBay for less than 1000 gbp..

Any advice on how to go about it would be highly appreciated! Thank you