Finally bit the bullet and ordered a replacement rear tire yesterday....where the leak showed externally did not go through, apparently air was working its way around to escape.
I needed a new lawn tractor tire (rear, 18x9.5-8 NHS), ordered one through Amazon; it arrived with clear tape holding on the shipping label, but so tight it deformed the tire. I had tried plenty of Slime, could not do a plug or patch as it appeared that the hole only went through to the inner plies, then leaked somewhere else.
Anyway, like most of us, I reviewed Google and YouTube to figure out how to replace the tire. Let's just say that it was a real challenge, both getting the old tire off, getting the new tire on, and setting the bead/filling with air, and did not go as readily as it did for the guys in the YouTube videos. Because the tire was deformed in shipping, I could not use the rope/strap technique to seat the bead, was fortunate to get that seated and filled with air.
I would say the process took almost 3 hours over two days, removed the old tire first day, the remainder the second.
If I need to ever do another one, I will consider a tire changer from Harbor Freight.
https://www.harborfreight.com/search?q=tire changer