Im sorry your little man has had such a tough time. It would be useful to see a picture of this protrusion from his scent gland. Sometimes they can get infected, or even develop growths.
In terms of diabetes care, I only use electrolyte solutions for ketotic diabetics (and I mix a sugar free version, even though by that stage my diabetics have been on full dose medications). I have used glipizide-a prescription medication- with my diabetics which I feel has helped their symptoms when diet isn't enough, for example drinking excessively or being grouchy due to high sugars. Some people use fenugreek though I found it difficult to titrate the amount, and although herbal it still has potential serious side effects. I always recommend seeking vet advice before using medications or electrolytes. As well as diet, I have cleaned weekly with wet corner spot cleaning in between.
For end stage diabetics I have made sure they have a water bowl as well as bottle (I used coop cups) as I found they struggled to work the ball bearing. I gave them more treats in terms of baby food as by this stage strict diet control wasn't going to make a big difference (and my hams were already on top dose oral meds and insulin isn't an option in my mind). Some died suddenly, some of overwhelming infection and one of a neurological problem. Each has been an individual so I've tailored what I did to the ham. There's more diabetes info
here including references if you see a vet who wants more background, though feel free to pm me if you need.