Well, I would be putting a dressing on that all the time.

Change it daily. Something cushiony --let the podiatrist recommend something.

Zinc is a great healer... perhaps Alan needs some oral zinc?
This is given typically to people with bedsores and other hard to heal wounds. You have that zinc at home anyway still?

Also l-arginine helps too. In nursing homes there is a drink called ArginAid but you can give Alan tablets...same thing. This heals skin wounds/ulcers. Vit C. Also.

If you go to a wound center they have special dressings that you leave on for days... and are designed to help the wound build a matrix of tissue for healing. They are very expensive, so see what would be needed, and call your insurance to see if they pay for it. Since Alan is not diabetic there may be resistance for them.

I would not let this wound be leaking into socks. I would be putting a sterile pad on it. Some wound healing products have silver in them. But since Alan is allergic to sulfa, the typical silver sulfadiazine cream cannot be used.

I think he will need to go to a wound clinic. These are more common now, and very useful. It is a miracle he hasn't had a severe infection yet IMO.