Hi ken. I am not sure if you have some insider information and i am not sure what you mean by 'heavy' but I don't agree that the OM system was not designed for 'heavy professional use'. I may concede that they may not have been designed for 'ham fisted (north) Americans' (I have added the 'north' to include us occasionally ham fisted canucks.)

In fact I remember olympus making much of the use of the om1 as a favorite of war photos in the Vietnam war where the size of the kit mattered.

So to recap, I am not saying they are as or more robust (or less for that matter) than nikons of the day, but to clarify that it was intended as a pro camera. Pound per pound they are certainly durable, as my original om2 (which bounced around India with me in the eighties) can attest to! ;-)