I had the same leak from my 2020 (and have spoken with others that shared the problem). The official explanation is that it's the result of a porous casting. Apparently, they send the case (after disassembling the bike completely) to be impregnated. I spoke to a number of folks that had it done and are satisfied with the fix (or at least the bike doesn't leak anymore). I also know of people that have had their bikes completely replaced over the issue. If you have a solid dealer technician, then I'd feel confident in the fix. With that said, it's a bit of a nightmare and you're looking at months of downtime. You should by all means be negotiating with Hinckley for additional warranty time at a minimum, and they should be throwing some goodwill your way, as well. I'm not familiar with Thai consumer law, however, so your mileage may vary.
I'm not in any way knowledgeable to the ways of metallurgy or mechanics, but it seems that if it was a porous casting, the leak would not show itself in the exact same place every time.