well, i have a good one i am dealing with and can use some expertise from some who may have lived a similar issue..
115 hrs only. all original...

cylinder 3, has 165 compression. it gets spark + fuel.
the plug is always wet.seems like it isnt burning the fuel.

then the starter broke it's plastic internal gear.
we believe it hydro-locked on fuel that went un-burnt and forced the starter to give away.

seems like the exhaust valve isnt opening..
can it be the rocker that loosened up ? and the push rod isnt doing it's job ?
.i seem to hear some minor internal minor noise only when i run the motor with that spark plug connected. when i run the motor with that plug not connected to the spark wire, runs smoother..

again, it seems...

did anyone ever have any similar symtoms on their 496 ?

Maybe it wiped the exhaust lobe on that cyl? Pull the valve cover and crank it over to see if it's moving, and how far.

Could also maybe be a stuck open injector? Maybe try swapping that injector to a different cylinder to see if the symptoms follow that injector.

Removed the valve cover. Found a rocker where the push rod went right through ! What could have caused this ? The exhaust valve wasn't opening...
What could have caused this ?

had a similar problm,with over fueling,,,did the same as yours,,,push rod shot out past the rocker arm,,i heard a ping while i was trying to start it,,,,a new lifter fixed the problem,,,,,when we tested the old lifter,, the plunger would not push into the lifter at all,,,acted like it was a solid lifter