I don't see anything in the original post to make me assume any kind of "Super Diode" has been installed, or that he wants it returned to "STOCK" with that considered I think first re-installing the original control would be a good place to start. If indeed you do want to reverse the procedure then the previous post maybe correct.
observe the original position on the wires, which is Orange, Green, Black on one of the Grants I have here (looking at it from the back) and simply reinstall (solder) the original back in place.
If your clarifier range has been greatly increased (more +-6) that maybe indication components may have been added/changed, IE Diode, or Choke. However this still has NOTHING to do with whether you can reinstall the original control or not.
If this doesn't cure the drift problem, then you may have to look into how the clarifier mod was performed.
Personally I've never had an issue with a Grant XL drifting, could indeed be a bad 10 turn, or it could be how the modification was done.