What oil do you use on your primary chain on your 1987 harley?

we use the same fluid as the engine oil.

As long as it doesn't have friction modifiers, engine oil is fine. Oils with friction modifiers might make the clutch plates slip. You can tell which oil has friction modifiers by the starburst symbol on the container. Usually 10-30 or lighter has friction modifiers; 10-40 or heavier does not.

ATF type F works fine, and you can tell if you have an engine or primary leak by the red color.