I have only seen this problem on the older diesels due primarily to vibration and shake from the engine. The clamps that hold the cooler hard lines to the engine block have plastic inserts to keep them from chaffing. Over time these plastic bushings break out, allowing the clamp to rub and wear through the metal line. When this happens you can experience a major loss of transmission fluid.
Problem & Solution
Common among these chassis:
In the picture above you can see the location of the clamps. On most diesels there are two on each side of the engine along the top of the oil pan. Check these clamps once a year to make certain they are tight to the line. If the line is loose in the clamp inspect the surface of the pipe for wear. If the pipe is not worn too badly you may be able to save it. Replacement lines are only available used or from Mercedes Benz. To fix the slop, take a short piece of thin rubber hose, slit it down the middle and make a new "bushing". Rubber will last a lot longer than plastic.
Here is what a damaged plastic bushing looks like:
While checking the hard lines (pipes) be sure to inspect the transmission oil cooler flexible hoses at the bottom of the radiator. If they show any signs of cracking in the rubber or wetness then replace them. If the lines are leaking at the fittings on the transmission then replace the banjo fitting washers.