What To Do When Your Dog Is Dragging His Butt - Now It's Simon's Turn

I've written extensively about Alvin's anal gland issues and his multiple trips to the vet to remedy the situation. See these posts:
Part I of What To Do When Your Dog Is Dragging His Butt
Part II of What To Do When Your Dog Is Dragging His Butt
Part III of What To Do When Your Dog Is Dragging His Butt

Now it's Simon's turn to drag his butt. At least I have a little experience in this "area."

Simon's been scooting on and off for the past 4 days. When we first noticed it, we had friends over who know how to express the glands. We tried it and nothing happened. Then we cleaned his anal area and applied an antiseptic approved by the vet because it looked a little inflamed from the scooting activity.

Poor Simon - this morning I noticed him dragging his butt on the kitchen rug. This time expressing the glands produced some fluid. I cleaned up the area using a pet wipe. We need to keep a lookout for more scooting.

The question is - when does butt scooting require a vet visit? We took Alvin in after a week of discomfort. But with Simon the glands can be expressed, so it's a day-to-day watch and see.

What I don't understand is why the glands are not self-expressing as they should. With every bowel movement, the fecal matter should be sufficiently solid to push up against the glands and release the fluid. It's gotta be a diet thing.

We have a good relationship with the Boyz' vet techs, so I might just call in if things get worse. Sometimes they talk through the problem over the phone.