Don't purchase dogs from pet shops or " licker stores!" Sorry, couldn't resist. My dogs lick each other alot. Does he have toys to chew on-maybe get him a large Elk antler to distract him from the licking. It is probably an ocd habit. Need something to distract him from it. Or a kong with peanut butter, or some treat in it.
Any kind of peanut butter will do. I have recently found uncooked bones that I give my girls and they eat the fat and bone marrow out of them and I replace the center with peanut butter and they love it. The bones are beef bones of a good size I give to them raw and the center hole is great and just the right size for smearing peanut butter in them. I use creamy but have used crunchy too; the creamy adheres to the bones better. Good luck.