[Revi16]

Being somewhat familiar with American V-12 and radial engines from WWII it seems unlikely that a Bf-110 would need an auxiliary oil system for a 5 hour flight. Most V-12's (when compared to radials) don't use much oil during operations.

I've read that the Bf-110 had a 35 liter(9.25 us gallon) oil tank per engine. Even if using 1 gallon of oil per hour, 9.25 gallons would be sufficient for a one way flight.