Basically the inserts are the sleves on the cases that the bearings get pressed into. the bearings might be fine but sounds like there is wear which allows movment between the bearings and the sleeves. How to replace them is you send it to Jerry hall at Halls Precision Racing and pay him money to put new inserts in.
and what he'll do is cut out the old worn inserts and press in and weld new ones. I dont know of anyone who does those themselves but it might be do able.