Size of a pin (what?) I, for the life of me, can’t figure out what that censored part could be. But it has got me curious. 
So regarding the grooming: Hmmm. Have you noticed a change in his hay intake? i know that sometimes excessive grooming can be due to lack of fiber. Of course, I absolutley know you have enough hay for him, but I am just wondering if there has been a change in the hay at all which has caused him to eat less, and then therefore, compensate with grooming (the thought is they overgroom as strange way to get “more” fiber). Do you notice he grooms himself more at all?
Also, sometimes bunnies will focus on something that is wrong with the other bunny. Jack will clean Rucy’s blocked tear duct so well, that I don’t have to do it, but every once in awhile, when it gets time of Rucy’s tooth trim and her eyes water more, Jack will lick too much. Usually Rucy leaves, so no great damage is done, but I am wondering if there isn’t something in the area that Kramer could be focusing on.
??