I have a new to me Yamaha VT480S. Looking to change the chain case gear oil. Manual calls for API GL3 75w or 80W gear oil. GL3 oil is no longer available. GL4 and Gl5 75-80W Oils have sulfur that I've read can damage brass and soft metals. I've also read modern GL5 oils will not corode soft metals. Not sure if this sled has soft metals or brass in the chaincase What oil do I use in the chain case? Only GL3, GL3 and GL4 or GL3, GL4 and GL5. Thanks! ~Kevin.