Although opposed by some members, I would start with an oil and filter change. The dealer here not recommends, but imposes an oil change on 722.6s every 30,000 miles. They have seen more than a handful of failed 722.6s with less than 50,000 miles on them.

After that, if the problem persists, have the transmission electronics checked (it is usually one of the first and few things to give problems on 722.6s). Besides that, the transmission is very reliable.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]