Hey Clarion,

For starters, got to check the oil level with a testing dipstick, and the oil quality...

722.6 dipstick | eBay

Next, physical thing you may do. Find the TCM(transmission computer) unplug the connectors, and look at them for oil contamination as it super common to see this.. Look at this thread on post 5 if you find oil in the TCM it is the result of failure of the o-rings on the circular connector-post 1.

My attempt at replacing the transmission plug. - Mercedes-Benz Forum

The TCM can be cleaned with contact cleaner. Do about six intervals of spraying, and pat-drying with paper towels, and on the last one pat-dry it, and let the TCM dry overnight standing up...

Do get you codes scanned too..

The fluid you can use is Valvoline Max-Life ATF in the red jug from Walmart...

All the best

Martin