Are you familiar with the Scattergun sling?
This is a little hard to describe. The sling has a J-hook piece of steel on the end that goes through a slot in the side sling adapter which is a flat piece of metal. There's a piece of bent spring steel in the J-Hook that closes off the J but is flexible for installation purposes. Unfortunately the spring steel catches on the flat bar which forces the spring steel apart like a wedge.
If the side sling adapter was a conventional ROUND bar there would be no problem.
I'm afraid this is one situation where duct tape won't save the day.
It wouldn't be able to keep the spring steel from being wedged out by the bar -- too much leverage.