they need to take it back & send you a good one. I ain't familiar with those dists but I sure thought it was too good to be true that the reluctor/magnet gap does not change when the can is applied (but if they have solved that then kudos to them). On OE dists it (vac adv) drastically increases that gap (in addition to the RP change) which does affect cyl to cyl timing.
The advance plate on the firecore distributor is solid, much better then the factory advance plate, I can vouch for their advance plate not moving when the vacuum advance is applied. All 8 teeth remain the same gap with vacuum advance applied, the issue is the bearing between the shaft and the housing causing the shaft to have a lot of radial play. But ya read my post above this one, he was kind of a duech on the phone and made him self look pretty bad by saying he had never heard of rotor phasing and that I caused the radial play by installing a different reluctor.
