Someone tell me why the seals won't fail in the same way that Wankel rotors in the RX-7 do--but it will be a lot of fun until they do!

My guess is because there's only one set of seals in the case, not a second set for the "piston", and so there's no seal to seal scraping. The smooth shape of the "piston" and lack of corners should minimize wear.

suck, squeeze, bang, blow

NSFW

This response seems to have a few gaps in it, but here's what a company rep said:

"And then there's our apex seals, they're like our piston rings," he continues. "In the Wankel engine, they're inside the rotor, again. They move at a high speed, and bounce around, they're very hard to lubricate. In our case, they're stationary, they don't bounce around, and you can lubricate them directly from the housing.

"So we basically solved the key challenges the old rotaries had with combustion and with oiling. Those oiling challenges caused both durability issues and emissions problems. By making those components stationary, we solve the challenges of the old rotary. And we also upgraded its cycle to give it much higher efficiency."

https://newatlas.com/military/liquidpiston-rotary-x-engine-army-generator/

"How is the engine going in durability testing? "We've been hyper-focused on proving the general operability, and showing that the engine works in these application demonstrators," says Shkolnik. "Now that it's pretty apparent that it's working, everyone wants to know how many hours can it run. We're working through that, it's part of what we're going to be doing over the next year. We're running engines for tens of hours, dozens of hours, we're not yet in the hundreds of hours where we want to be.

"We're not even running them long enough to think about things like seal replacement yet," he continues. "It's been a combination of little things we're addressing as we go along. "

Hmmm. So, not an actual engineer--why would a seal that's in the wall and has the rotor spinning past it do so much better than a seal which is in the rotor and spinning and spinning past the wall?

Increased lubrication and stability.

Liquid Piston Rotary Engine - In Slow Motoin has been added as a related post - related requested by newtboy on that post.