There is little chance of a fix that you can do for the problem you
describe unless you have a lathe.
There is a way you can identify the roller with the problem. Get a
dial gauge and a magnetic base and set it up to monitor one roller
and then the other. An inexpensive dial gauge (like one from Harbor
Freight) will normally have a an accuracy to 0.0005 inches and the
error you are looking for will probably be in the range of about
0.010 to 0.020 inches on a full gauge thickness at larger gauges and
in the smaller gauge range then it will run 0.001 to 0.005 inches. If
both rollers are off, and it has been your luck to have them mated
this way, try rolling the follower 180 degrees from the other to
reduce the error. This will not 'fix' the problem but it may reduce
it to a livable level.
Write Durston customer service and go through the setup and
alignment with them, and they will then see the problem you are
describing and should have you send the mill in for
repair/replacement or send you new rollers. Either roller could be at
fault but at least one face is not concentric to the shaft. A bushing
cannot produce the symptoms you describe.