I keep the supplied one for head oil as you don't need to tip the can up to fill the head or apron gearboxes. For way oil I use a small Reilang can that suits the ball oilers and works well at any angle without leaking
All my oil-cans leak, some worse than others. People say nice things about Reilang but they ain't cheap. Not much should be expected of a vintage oil-can; think "worn-out" rather than "quality".