Thanks for this write-up! My trans went from chronic failsafe warnings to getting stuck in my driveway but this helped me get the ball rolling in diagnosing my issues.
Knock on wood as I'm not sure if I'm 100% outta the woods yet but I let a buddy do my trans, diff and transfer case fluids yet I still got tons of transmission failsafe warnings to the point where eventually I had to stop driving the car and it's sat on my lift for over a month as life continued and I just drove my 328.
Long story short I discovered my buddy didn't replace the 4 sealing tubes, which I'm HOPING was the issue w/ my logic telling me that they'd shrunk so much that they weren't sealing, causing it to lose fluid pressure, hence my random slamming of gears, randomly flashing P on the cluster and getting trans failsafe even sitting in park. Bottom line though...replace the Mechatronics sleeve, Mechatronics gasket and do NOT skip the sealing tubes...it's only an extra $16 and to this day I still don't understand why he'd skipped something so menial even though he already had to drop the valve body anyways.
This is one of a few videos of my trying to diagnose my issue within the car. I spoke with multiple different types of shops, anything from repair places to transmission and diff rebuilders and was told anything from ignition coils and/or alternator causing voltage spikes to the transmission and/or transfer case needed rebuilding since I got tons of transfer case codes.