Hi Nick,
I use both (for X and Y). They actually work exactly the same. The one with three wires has one unused. People from Flytech told me that the Aircotec one is just a copy of theirs.
If you need one, I can ask the local paragliding school if they still have some left. They used to have a couple of old ones. But be careful if you want to use it with a recent flight computer. It didn't work with my XC Trainer.
I wanted to use the plug to make a second serial cable for track download, but internally, they use different pins. The ones used for serial are cut off from the sensor cable.