[U]100psi across both rotors and all 3 surfaces?
[/U]At what RPM was this tested? Its useless without RPM figures. But judging by the car's model, the RPM was probably close to 250rpm (as it has the upgraded starter motor). Even after correction, your car's compression is basically very little.
Even if we take it to be a corrected 100psi @ 250 rpm, that's ~6.8 bar which means your engine is on its last limbs. 98.6psi is the MINIMUM spec that Mazda says is acceptable.
However per my experience, when the engine falls to around 100psi of compression the following is already happening:
- Decomposing water jacket seals
- Apex seals at 20-30% life
- Chromed rotor housings meaning very little life remaining (5,000 km at most)
- Corrosion around water jacket channels (meaning coolant leaking steadily into the housing)
But the flip side is, if you rebuild the engine now, you can most likely save your rotors which is about $1300 saved. A rebuild at this point (with reused rotors and other basic parts) is about $2,500 if done with new housings, seals etc.