I am sorry to hear about your pup, Thorn's, anal gland problems.
He may have deep, difficult to access glands that don't empty as they should when he passes stools.
This is a common problem for dogs and seems to be more common in overweight dogs that are fed lots of table scraps or eat a diet low in fiber. These glands are normally expressed when passing stool but if he eats a diet low in fiber his stools may be too small or infrequent to empty them. Or if his glands are anatomically in a deeper than usual position they simply may not empty as they should no matter how much fiber he receives.
I recommend weight loss if he is overweight.
I also recommend decreasing or stopping entirely table scraps.
There is a product called "Glandex" that purports to help. I don't have any personal experience with it but here is a link if you'd like to read more about it. https://www.glandex.com/
You may have tried to add fiber but it may not have been enough. A diet higher in fiber, such as a weight loss diet or mature diet, may help. Sometimes a prescription food very high in fiber like Hills r/d or Purina Veterinary Diets OM is needed.
Some dogs with food allergies have perineal inflammation and irritation and that seems to stimulate anal gland secretions. Sometimes a true prescription hypoallergenic diet such Hills z/d or Royal Canin limited ingredient diets is the answer.
Another possibility for perianal inflammation and increased secretions is a condition called a perianal fistula. These pups have full anal gland that are uncomfortable and cause scooting and licking but they also have painful cracks and inflammation around the anus. This disease process is more common in German Shepherds but any large breed, thick tailed dogs can be affected.
If his glands are continually full but not infected you may also want to ask your groomer if they will empty them for you weekly to every other week. You can try to learn to do this yourself, but most dogs aren't overly cooperative and it is usually a two person endeavor. It is done by gently pressing and pushing/milking out the secretions with your gloved fingers at about the 7-8 & 4-5 o'clock position around the anus. Here is a link if you want to see how it is done: https://www.youtube.com/watch?v=T4tiz27F5do
And of course if all else fails removal is an option, but given the possible complications (infection, strictures or incontinence) I recommend this only as a last resort measure, so hopefully some of these suggestions will help.
Best of luck with Thorn, let me know if you have any further questions.