Ok 2005 MT, 97K, well maintained, no major issues ever. I go to start it yesterday and the engine spins like there's no compression. It was running great when I parked it the night before. Can the apex seals fail suddenly like that?

There's no reason it should be flooded, and I've never flooded it. Ever. But after reading several posts I thought maybe that could be the problem. I did the Mazda de-flood procedure, no joy. Plugs were a little wet, but not dripping. Not much came out of the plug holes when I cranked it without the plugs installed. I installed new plugs anyway since I have extras, but still no joy.

Tried to pop start it down a super long hill... nothing. Engine just spins, again with almost no compression.

Time to get it to the dealer before 100K?

 

A non-firing ignition system can also feel like there is no compression.

 

^^Like he said. If it was starting and running fine before, Sounds like there's no spark or no fuel. Check all your plug/coil/wire connections and check for spark. And check your fuel pump fuse. I feel like your fuel pump fuse is blown, or your pump has crapped out.