I don't see them come up for sale very often (the 78G .22) is more desirable, but I would say they will be in the upper $200 range. A good condition Crosman MK1/MK2 which is much more common will bring $200.
There were a lot that "blem's". Metal finish issues, stock less than perfect..... They were available from several sources at the time, I remember seeing them at gun shows back in the day. The sellers never mentioned that the weren't the real deal.
Paul, like other tuners of his caliber were overrun by people that had no idea of what is involved in a true tune. During that time frame there were many "shrink tube" tuners that would turn a gun over in a day. Paul and JM just got tired of the uneducated air gunners. I have this from the source.
Back in the old days you could call FX USA and that would have been taken care of. That is a factory defect! Now days the representative will say, "Well we can sell you a new liner"