Forget the high priced "marine" oils. Use automotive hypoid 90 oil. it has the same specifications but is not supplied in the expensive squeezy tubes. I have used this oil in my Honda B75 which is over twenty five years old and still going! I might add that there is no abnormal wear on the gears. The engine has done thousands of miles around the inland waterways which must be a testimonial to both the engine and the oil. I use a "duck" type toilet cleaner bottle to insert the oil into the lower hole in the gearbox which is better than the original bottle. Just make sure that it is well washed out and dried before use.