Hi Alex,
Looks very genuine to me and a nice bullion version. Maybe your friend suggested it been a copy so that he could persuade you to part with it
As for the prestik/ticky tacky/bluetack, I have tried using some fresh prestik to gently agitate the old untill it becomes tacky again and then comes off. It still however leaves a thin layer of the stuff. You could also try and freeze the prestik with some ice and then gently chisel it off with a sharp scalpel.
I am sure there is a product out there that may clean it off completely, but I am not aware of it here down South.
Regards
Steven