The CF rating replaced the obsolete CD and CE rating, which is what the 30wt was in 1984 .They used to make a cf-4 oil that's for 4 strokes.there must be enough of a difference.
gear oil.
Use any oil that says “diesel” on it.
Hell, use any oil that says “oil” on it will work just fine lol.
These engines don’t really care as long as your not filling it with water or gear oil.