Just thought I'd join your forum and say hello and thanks for the info you folks provide. I worked as a tech at a dealership for 20ish years and now just tinker with these fine cars for my own amusement and enjoyment.
My most recent acquisition, a $1500 craigslist 97 S600, had me doing quite a bit of fruitless googling. I bought the car with a no reverse condition from a lady that couldn't afford to have the trans rebuilt or replaced.
Not only did this car have no reverse, it would also attempt to creep forward in neutral, not your normal 722.6 complaint. After checking and repairing all the "normal" issues. (the car had a broken valve body spring as well as leaking plug bushing with fluid wicking up the harness to the tcm). I pulled the trans out and disassembled it. (you can get the trans out of a V12 without removing the exhaust btw
) Anyway the problem was actually one of the B2 clutch fiber plates had fused itself to one of the friction plates (probably from a low fluid slippage situation due to the leaky plug bushing), putting the trans in perpetual forward and making reverse impossible.
The long and short of it is I could find nothing about a no-reverse condition on a 722.6 or NAG1 anywhere on the internet, so I thought I'd share my findings here. A rebuild kit later and I can't tell you how much I love that 600. I'm gonna buy all the $1500 dollar V12s I can find.