Sorry for your problems,

The lurching of reverse is the inside lip seal. It is hard as nails because of the heat, and eventually it will tear, and you will loose reverse completely. I have been there once, and I'm there with my SL320 with the same problem right now..It is a Under ten dollar seal right behind front oil pump..Photo 7-the inside one.

722.5 transmission oil pump rebuid DIY - Mercedes-Benz Forum

It is the same thing with the forward gear too. A hard o-ring too. The B2 piston inside seal is rock hard. This one you can get to it from the outside, but you may have to remove the transmission mount and use a jack to lower the rear of the transmission down a bit to push in B2 cover with your thumbs to pull out the locking ring..Look at the 15th picture in the bore-the black seal-replace the steel guide with the updated plastic one. I would change B2 piston too as the shaft is probably all wavy..

How to Replace Your Oil Cooler Lines

Basically, with these hard seals. I would bet you need other seals too, and your transmission is very overheated because of the large car.. These transmissions do need a separate cooler for these big cars.

Not what you want to hear, but I like repairing transmissions, and can be done by anyone who DIY's here..

Martin