Do a search on utube for harley problems. The M8 is garbage. The twin cam had problems. Last decent engine was the EVO. Prices are through the roof for a product that has known problems.
Rode a 51 pan for thirty years without ANY problems. Last bike a 06 for $14k cost me 2 grand for the chip and an exhaust system that didnt sound like a vacuum cleaner..
If I could still ride I would build a a pre 83 shovel wide glide 6" over in black...
Heres the twin cam problems. M8s are different problems.
https://youtu.be/YTEROhR-cEo?si=UztzvZ0cVXsWvVV7
The only real problems I've seen on Twin Cams are the tensioners for the chains. Those are pretty much a consumable, regardless of what they're in. Every engine manufacturer has them fail, it's a matter of how well you maintain it and how hard you beat on it. You can get rid of them with an S&S kit. You can also use high quality synthetic oil, and a good oil cooler and triple the life span.
The M8, that's another train wreck entirely. Those things have ugly oiling system issues, and if the valvetrain has a problem, it's really ugly. But they have some pretty serious power potential. You just need to get all your stuff from someone like George Bryce at Star Racing.
Both the Twin cam and M8 could have a crank problem, I haven't seen many of them fail though.
I really like my Twin Cam bikes. I wouldn't own an M8.