Although I don’t know much about 80-90w oil your talking about I’m sure it would work fine. I personally would use any major outboard manufacturers Hypoid 90 gear oil…it has additives to help with water intrusion. OMC,Mercury,Yamaha,Suzuki,Sierra..they all make a good gear oil. Mercury even sells their synthetic blend gear oil. I have used the Sierra gear oils for years with great results. And yes…same filling proceedures…fill from bottom to top vent hole.
