You aren't kidding about it being burried...I feel like I followed all the links and still can't find anything! ;)
We've got a little (non-OSC) UDP plugin that was written here, but it was a one off and had very specific, and limiting, commands that I am not sure I can make work for this application. And the UDP messages are to be 8 byte, composed of 4 16-bit integer! That's been a fun task to handle in java (given my limited java skills).
Just out of curiosity, where were your reliability issues? I've heard that MIDI is a crap shoot with Motionbuilder...but was hoping that a specially built plugin might be a better, and more stable, approach. Reliability is a big issue on this particular project I am working on (like it isn't everywhere, I suppose!).