Hi, everyone,
You could always try giving raw chicken wings for 1 meal, that is if you feed twice a day like me. Jess is 7 months and is fed raw and I have never seen this scooting action you mention. It must be quite upsetting for you and the dog to have to go the vets and be fiddled about with like this!!!
Anyway, rather than resort to surgery it could be worth a try. I know some people are horrified at the thought of giving raw chick/wings complete with bones to their dogs but my 7 mnth girl loves them and really solid poos that obviously do the job of emptying the glands. Jess has chicken wings every single day (normally 3 per meal)
If all else has failed maybe its worth a try.
Hope this helps
Linda and jess (p.s. her teeth are sparkling white too)