[Yosemite Sam]

The first question is; Does this PTO have a brake or is it the kind without a brake?

I don't know if I understand, "Mower almost died", did the mower almost die or did the engine almost die?

I don't know of any situation where the PTO would fail and kill the engine... Normally when the PTO fails, it either slips or won't disengage. Unless it has come apart and I still don't know if that would kill the engine.

It sounds like you have something jammed up under the deck.

I did have a belt come apart one time and one of the "strings" from the belt wrapped around one of the deck pulleys and nearly killed the engine.

If all else fails take the belt off and see if the pto is working as it should.