Good afternoon,I thought the same. I thought it was P400 vs P500 related, I thought it was worse in 5th and 7th gears, I thought starting the car and having to reverse while cold may cause it. Fact is, that wiring probably caused all of it. Yours may move when shifting hard on P500, causing you to think they're related.
I replaced every mechanical component including the whole actuator tray, pump, all of it. It was the wiring the whole time.
Not sure if there's a way to check the wires while the transmission is in but worth checking. My bet is they're shot.
Son of krypton - Your responses were appreciated. I still have the M5. Sat in the driveway for a few months and then took it to an indie who is a master mechanic because this car is man vs computer and computer is winning. He ran codes and 5506 came up again. Along with ibs. He asked to bleed the unit again to eliminate that being the issue. He bled it and retaught clutch and it ran for 5 days before red cog and stuck in 1st gear again. He tried running the sequence and it timed out in fifth gear numerous times. He believes like you said it is the wiring so he wants to drop the transmission. He said he ordered the wiring from Germany it will be here in four weeks. He is only charging me 2g to do the job. He seems legit but I have two questions. I don't have ista and my foxwell nt530 sucks. Do you think I should replace 1 or both battery cables? Should I buy a used smg ecu off ebay that has a "working" history? I don't have a lot of money and am thinking if the ibs needs replaced might as well do it anyway. Thanks for your time.