My Black&Decker Workmate 750 has always had a wobbly top.

The wider part (which slots into 3 different positions to allow a wider
range of jaw size) sits on two plastic bars each of which has an alloy nut
with a groove in the side to fit into a slot the metal frame.

In my case when the alloy nut is bolted through the wooden top and the
plastic bar the groove is slightly proud of the plastic.
It is the same on both sides.
This is cause by the contact between the alloy and the bottom of the hole in
the plastic not being quite deep enough to allow a flush fit.
There are two faces - a wide one at the base of the hex nut and another at
the base of the shaft.
Either one could be the cause of this (or both).

So the question is:

Is it meant to be like this i.e. wobbly?

Or is it meant to be a snug fit so that when the alloy nut slides back into
the groove the metal frame is gripped firmly against the plastic bar without
a wobble?

TIA

Dave R