gear oil

My MD22L has a reverse gear which supposedly requires just VP's own brand oil at $50 a quart!:yikes: I check my gear oil every 3 months and for the first time found it to be "Burnt" but still had lubricity. @Rich Stidger has the same engine and we have been chatting in a private message about...

My Suzuki DF2.5S obm calls for SAE90 gear oil, however I can only find Castrol Manual 80W90 gear oil. Can this be used for my obm gear box?