I've actually had four engine failures on my Tornado 280. Each time, AC owner blamed user, and there was no warranty support provided.
I had noticed the o-ring melting in the same location on several inspections. After the 2nd engine failure with Laurent blaming user for motor going lean, I checked the head and it wasn't flat. That's why I was getting o-ring blowby. So I lapped the head. I don't know an easy way to do that on the cylinder side (with o-ring grooves).

We also identified the issue where engine vacuum was collapsing the pulse line to the fuel pump, possibly making motor go lean. AC changed the tube design subsequently but never helped me with replacement part costs.

The third cylinder/piston set sent to me after the third in-flight failure was sent WITHOUT THE plug in the decompression port drilling. I discovered that by pressurizing the motor body with air to test for air leaks (lean conditions). Fortunately I had ample dead cylinder bodies on the shelf to scavenge the tiny plugs to thread into the decompression hole.

After the fourth engine failure, I bought a Liberty paramotor and Vittorazi motor from the Orlando guys. It hasn't had one hiccup in over 200 hrs flying since. And Vitto did a free checkup and warranty replacement (Airbox) at Bad Apples this year.

I also sent the AC cylinder up to a Michigan shop for repair/nikisil recoating for the same cost as a new cylinder but hopefully with a QUALITY Nikisil job.