My I point out another coupler with which I've had success.
Protomax by Walthers is a clone of the KD5 with a slightly bigger head.
I use them extensively without problems. And...they are about $1 per car.
You can buy a 20 pack oftentimes for less than $20.
20 pair, that is.
I despise the KD802. Surely KD can do better than give us ancient technology.