Kernow, my black lab does the same thing, minus the drool. My vet as well says nothing is wrong with her at all. It's just habit. If I call out to her, she stops and goes to sleep or plays or whatever, another indication that it's just habit or something she does versus a problem.
I tend to agree with Orrymain, I think it is just an annoying habit. My dog has one or two irritating habits, but there again so does my husband!
Thank you for all the advice and reassurance, it helps to know that she is not the only dog that does this.
Being that the dog is a border collie. My first guess would be that the dog is probably bored. They are extremely high energy. And need lots of exercise, they live to work (herding) so I would try exercising the dog everyday. And then see if the licking tapers off. It might take awhile so be patient.
I have a black lab that also is a compulsive licker. I've given her a Kong, rawhide bones and beef bones with frozen peanut butter in them to give her something to do with her mouth. With her it's boredom. She really gives the Kong a work out when she gets it. She's just a high, high energy dog.
She is a mature border collie, a lot slower than she was. According to the advice I have been given she is getting plenty of exercise and activities to interest her. It goes without saying that she is given exercise every day (at least twice) it would be cruel not to, she also has company and things to keep her occupied.
Both my boxers lick the inside of the car windows and the back of the headrests..........Ruby has done it from the first day we picked her up, Roddy watched Ruby doing it and decided it must be a fun thing to do as well............I usually call their names to distract them out of it.
This is just a random thought, but in humans taste and smell are very closely related, I womder if there is some connection for dogs too?