They are not very strong in a modern context. The M410 is stronger in theory but rare. Only fitted to a few p1800s.
In my experience the m40 and m41 principily fail first at the laygear rear needle bearing. The needle bearing is small for the load. Unfortunately the bearing face on the interior of the gear wears through the case hardening. I have thought about repair a couple of times but the metal is thin by design. Possibly spray weld followed by grinding and then cold hardening. I am about to build an m41 and have cold hardened the shaft and gear set, it will be an experiment. Once the laygear and bearing wear, the gears run out of alignment by a couple of of mm leading to point wear on the gears and then failure. Noise is the early sign.
I suspect failure is related to poor or low oil in many cases.
I would probably plan to rebuild periodically and preventively in order to maintain that rear bearing if I was going to use it in anger for a rally.
Parts are getting quite uncommon also