...that is indicative of a battery, connection, timing or tune up problem.
Yes, too much advance will also cause the Bendix to crack. Its not the gear itself, but the over-running needle sprag clutch that allows the engine to start without back-driving the starter motor to excessive speeds.
And what is the rational for only using the compensator only on electric-start bikes? I think that the Sportster transmission is so over-designed, it can take the shock loads from a direct connection, but the compensator would make the bike smoother and quieter, and I assume Harley was willing to take the weight and cost hit for the more "refined" XLH model. I suspect they tried the cheaper hard sprocket on the 1967 XLH, but the cracked Bendix meant that was a no-go.
Note 99% of engines either have little springs in the clutch plate that do exactly what a compensator sprocket does, reduce shock loads to the transmission, or a torque converter, that has the same effect. What Iron Sportsters have is a large displacement, high-compression, two-cylinder starting load, with a disadvantageous starter gearing, up until 1982. What my mechanic pal told me is that as the battery gets weak, the 45-degree advance means the engine would kick back since it was not turning fast enough. We have all heard an electric-start iron Sportster go grrr-grrr-grr-thump and stop dead even though our finger was still on the button. That is the event that supposedly would crack the Bendix clutch if the bike did not have a compensator sprocket.
Agree that at partial loads the compensator does reduce the peak torque, but that is for steady-state noise and smoothness, not the other function of protecting the drive-train. I stand by my warning that a 53 and 54 K was designed and tested by the factory to use a compensator, and welding them up creates a risk of damage to the tranny.
Hard to say where we can find more early compensators. We could always look at an adapter spacer to run the Sportster compensator in the 53-54 sprocket shaft, assuming the primary cover would still fit.