My 57's stk distributor would not adjust to correct or hold dwell readings. There was a problem with the advance plate pivot & it was touching against the vacuum advance arm. Obtained another unit, which was readily available, and had a friend clean it up & set it up on his Sun machine, with new points, condenser & vacuum advance unit. It reads about 28 degrees at idle, which is spec, but when the engine is accelerated drops back to about 21 degrees, which is well below spec. So, I thought about it & disconnected the vacuum advance. It then holds, only varying about 1 degree. This seems to indicate some wear in the bearing setup of the advance plate, or what is likely the trouble? Are parts available? Thanks..

Paul