Yes I think they should be agitated well before using. BUT, if you have such a large
quantity, send a sample after agitating to get it lab tested. They can compare it with the original specs for the oil. I bet it passes with flying colors.

Blackstone Labs comes immediately to mind, as does Titan labs. You're looking at something like $25 for a test. Or do a Google search for motor oil analysis and take your pick.

R.