It's not a "dipstick" in the conventional sense. It's a tool that is used to check/set the fluid level, and then removed.
As such it is common for all 722.6xx transmissions. The ones on ebay seem to be fine, like the el paso tool folks, for example.
Note that you also need a reliable way to measure fluid temperature, as that is a critical factor related to fluid level.
For more information (probably more than you want) you might have a read through the 722.6xx FAQ thread located in the W210 forum help/diy stickies.