"- weight"

They don't post any specs, but it's supposed to be smaller than traditional motors. If it only needs a small amount to fill small gaps between disks, it might still be lighter than traditional motors. This is especially true if the PCBs are significantly lighter than windings and magnets.

"- leaks: liquids are always a hassle in things that move. The liquid wants to escape and will do so at the first opportunity."

Sure, but this seems like a small concern when we consider that any mobile electric motors require batteries and most of those contain sealed liquid. Even things like bearings in cars are sealed these days.

"- serviceability: if there is a leak and a significant loss of fluid, this doesn’t sound like something I can just go pick up at the hardware store like motor oil or hydraulic oil. I’m curious what it is… they simultaneously call it a commodity fluid but also proprietary."

Sure, if you have an oil leak in your ICE car today, you can't just go get oil, you first have to fix the leak. Don't forget that many transmissions for cars today get filled with "lifetime" fluid and are sealed. This, like the other concerns, is not likely to occur frequently and is consistent with existing paradigms.

I'd be more concerned with what it is rather than it simply being there. Like is it flammable, acidic, caustic, or hazardous in some other way?