I agree with Reno, the marks are probably aluminum oxide or galvanising zinc-metal marks rather than actual 'oil', which would wipe off easily with dish-soap, if it were visible anyway. The makers will use some kind of die lube when forming the sheath, but it's more likely to be stearate powder or talc. The answer of course is to not mark the wall in the first place, by feeding the stuff out of a polythene bag or sleeve. Work smart, not hard. You are not getting paid for chores like cleaning up avoidable marks, which = less profit & less time with your feet up twirling a martini as the sun sets.
