The engine is shrouded so it isn't in the breeze and not spinning at all; at least that has been the case for the several times that I've seen a 5th egine fitted to 747s (one of the few planes with this capability -- out of necessity, the original 747 engine was so much bigger that it could only be carried this way at the time, decades ago). Planes parked long-term have shrouded engines too; clearly spinning without the oil pumps active is to be avoided Interestingly enough most 744s are not fitted for 5th engine transport (most airlines prefer to ferry the damaged plane back on 3 engines, without pax, instead) ... QF is one of the few airlines that has 5th engine capability on all of its 744s. It was common on 742s.

The drag penalty from that 5th engine is huge, I used to know the number but forget it now, but it was over 10% -- astonishingly large. There must be fuel balancing issues also (but the 744 has a sophisticated fuel balancing system).