Mike,

What year and style oil bath air cleaner?

Maintenance - 1948 Heavy Duty (Oil Bath) Air Cleaner

The filter element is not replaced in a 216/235/261 oil bath air cleaner. You clean the filter element in solvent/kerosene/diesel-fuel (the filter element is part of the top of the assembly), then empty the dirty oil from the base, and then add 50 wt engine oil to the base (up to the "oil" line in the base).