Aerotech,
"Shear sections" on drive shafts are put there to protect the component being driven, from being damaged when normal operating conditions are not encountered. EG: cold oil being too viscious and rotating the pump will cause unecessary damage to the pump.
The shear section also protects the component when you loose oil/fuel for lubrication. Thats good coz you fix the leak, replace the broken drive shaft and carry on. Thus saving an expensive bill to replace the damaged component.
As for how often this happens, depends on how old the part is, how much money you spend on overhaul(cheap overhaul means cheap job done), and the culture of standard practices( she'll be right mate type attitude).
As for "de-oil solenoid", now thats the guys who made the engine, found out that the starter was not "grunty" enough to ratate the engine at a sufficent speed to get it started without other problems. Having air in the oil reduces the friction on rotating the engine.
So bascially "shear sections" mean what it says. they are a design feature.