Wrap up.
Finally pulled the hub with the runaway dust cap. Found the bearing race for the outer bearing (which was originally pressed in place) flopping around madly in a groove it had worn in the hub. This would eventually have resulted in a hub failure identical to what had occurred the year before. I replaced all three remaining Alko hubs with the same Dexter hubs as the original failure. The Dexter hubs are MUCH heavier than the original Alkos.
I don't know what I may have done or not done to cause this. I replaced all the bearings three years ago. The ones on the right side failed, the ones on the left were fine. (but I changed the hubs anyway)
Made it here to my daughter's place 400 km/240 mi from home with four wheels WITH dust caps still under it and all bearings cool to the touch.
:B
(i think there's a beer left......)