the led flash lamps are designed to run on 12v but the flash circuit is 24v.  

not good for the led flash lamps.

the circuit in the pinballs have a resistor to limit the current to the incandecent lamps so they don't die after 3 or 4 flashes. so how long will the led flashers last?

Beaky, for the sanity of all concerned there is no way I'm getting into another detailed LED discussion with you  

The series resistor will drop the voltage to the flashers, either incandescent or LED.  On the schematic I've browsed it's 8 ohms with two more globes in series after this.  The globes are about 3 ohms each so sounds about right.   The parallel resistor is, I reckon, to keep the globe warm, so they don't blow on firing. To me it's a bit, but not really, like a soft start feature.  It's this parallel resistor which, if present, will make the LEDs shine.