The sludge trap , or oil tube, was introduced when the large journal crank was revised to the type with 3 radial flywheel bolts in 1957.
Below is a rather poor copy of parts service bulletin GA2 date unreadable, showing the part numbers for the original small journal A10 crank, the original Road Rocket large journal crank and the revised large journal crank, together with the engine numbers when the revised LJ crank was introduced.