In my quest to convert a C304 to electronic speed sender, I found some threads on here that used a certain part number, but it only seemed to be available in Germany, if you could even find it.  I am in USA, so this is not ideal for me.  However, doing a lot of research online, I have found a part that fits the C30x transmission, and provides an electronic signal, that also seems to be available anywhere!  Here is the part we ordered:

https://www.ebay.com/itm/Speed-Sensor-For-Benz-Vdo-Man-0055429417-0065424617-2155-0100000-00995421017-/162664251844

I know, the quality is probably not as good as a German built part, but hopefully it will work for our needs, and it was only $12!!  It also has a Mercedes part number on it, which is 005.542.9417, so maybe it can be found from a MB OEM parts dealer??

The only bad thing is, its kind of big.  I had to loosen the parking brake shield to fit it in, and also grind down some of the plastic top end so it wasn't rubbing.  It is a very tight fit, but it fits.  Here are some pictures:









Hope this helps someone!!