Change ML320 transmission fluid
I only jacked the 1999 Ml320 up about 6" on one side and also used a jackstand. Sliding a screwdriver under the rectangular black access cover at the bottom of the bell housing, I popped it off. My digital camera with video cable then slid under the open port with a bright trouble light alongside and I visualized the transmission side of the torque converter.
I placed a 17 mm hex drive socket from Harbor Freight in the center of the harmonic balancer reaching in from below without any shroud removal. From above, I slipped a 1/2 ratchet drive partway into the socket as the 5/8th" protrusion of the hex was a little shy. Chalking a reference spot on the balancer (pulley), I rotated the crank until the converter drain plug came into view on my monitor.
The hex drive set included a 1/2" drive 5mm Allen wrench which I tilted to the back of the car when I inserted it into the converter drain plug. There's about a gallon of fluid to be drained. You might want to buy a new drain plug with crush washer or heavy blue Loc-tite goop but I didn't. Replace the plug and the access port cover.
Having drained the converter, use your 5mm Allen to drain the tranny. The tranny pan is held on by 6 T30 fasteners which pass through special spacers insuring you cannot overtighten and distort the gasket on reassembly. 2 corner spacers are different from the others.
Put some wood under the pan so it comes down level and does not spill the remaining fluid.
Yank the filter out. Clean the pan. Replace the plug.
I bought a filter and gasket from O'Reillys for $17 and preferred the crossed double retention tab over the stock single. Fit the filter into position and whack it with the flat of your hand under the tab to seat it. Now whack it under the metal tube with the O-ring to snap it into position.
Add a small magnetic grate in one of the interior depressions of the pan near the drain if you don't have one. They cost $7 at MB and are about 1"X2".
Fit the gasket and replace the pan, tightening the T-30 fasteners snugly.
The filler/dipstick tube has a non-removable cap which I removed with brute force long ago (it was unnatural). I think I bought a replacement removable cap as mine came off easily enough just now.
My measurements of fluid are imprecise because I made an irrelevant filling and draining mistake. The manual says 8 liters but that includes the cooler. I think I used 7.
Put a funnel in the filler tube and add 6 quarts of precious MB fluid which you can get on EBay for $12 each. Now start checking the fluid as you add fractional amounts to avoid overfilling.
I got a cheap Ebay dipstick and it worked fine. Motorcycle brake cable might work. The trick is, you have to bottom it out without bending it because measurements are made from the bottom up.
There are 2 marks defining a 176 degree normal level zone. My original factory added fluid just reached the lower mark after dinner (body temperature), so that's what I went for.
The dipstick goes in about 35" but you have to stop, without bending the bottom 3", when it bottoms out. The 176 degree zone starts 2.2 " from the bottom and extends up for another .45". I guess I'll check it again after driving up the Pass on a warm day. As I mentioned elsewhere, my old fluid had 211,00 miles on it, was thick and dark, and smelled of sulphur. I would identify it as hypoid gear lube and it is supposed to last forever. I only changed it to look for debris or other indication of imminent failure. I found none and hope the new, expensive thin fluid does as well.

I made my 3,500 mile drive without incident. However, I brought a good luck piece with me: a used transmission with a good pedigree which I had serviced. I should have brought the torque converter too as they are hard to clean after a failure. I cleaned the used tranny, put plywood plates on the ends with handles and chained it where the little back seat would go. My relatives were impressed at what a Boy Scout I remained at my advanced age.