I too was wondering about the valve stem seals. These diesels do not normally suck much oil down them. Your unusual loading might be a contributing factor. If oil consumption is less than 1 quart in 1k I personally would ignore it.

The only other thought I really would have to sit down and think about is. Would this usage oil increase under that senario or lessen if the oil passage on the frontal head area were a little leaky. There is not much gasket material between that passage and number one cylinder.

Again I would have to really roll that around in my mind before I could discount it or confirm it as a possibility. Initially I feel it is not a consideration but.

Over time if this engine exhibits much more smoke and higher oil consumption that is where I would look. Those 603 engines have always had a problem in that area with their head gaskets. A lot of gasket and head redesign was done over the years to try to lessen that problem. Cannot call it a chronic problem exactly but it can be there.