All IDEAL windlasses use 90WT. gear oil.

Horizontal windlasses have a pipe plug in the front cover of the gear box. Oil should be to  the level of the plug.

Vertical units have a pipe plug on the side of the gear box. Oil should be to the level of the plug.

The entire gear box is not filled with oil. It is just an oil bath.

Oil should be changed every 2-3 years.