On my "ex" a Cummins 6BTA, I never had to add any except at coolant change time.
On my current Ford-Lehman, I maybe top off once during the season now that I found and fixed the tiny leak I had.
I usually do a visual ER inspection the morning before a run. (I avoid crawling in a hot ER if I don't have to)
2 drop of oil after a 5 hour run is likely not a cause for concern, HOWEVER I would try to find the source. If something simple (like a valve cover gasket), I'd fix it. If something more involved (such a main seal) I would monitor.