I own a '91 190E 2.3 with the 733.408 tranny.
I had an out of the blue failure with only 112k miles on it.
Just like R Leo said, in my case the B2 band went out. I'm assuming that's considered part of the "front clutch pack" R Leo mentioned.


I could go forward, but not reverse. The B2 Piston on slightly older model 190E's and other benzes seems to be a sudden problem too. In my case, I was hoping the b2 piston would be damaged, but it was perfect. The b2 band had worn out.
So if you're wondering if you should just replace or rebuild before it leaves you stranded, I'd say definitely if you've got the money. I got stranded in the desert and had to hitchhike 200 miles. It sucked!