I also have an old wing. Mines a '82 which I bought 2 1/2 years ago.I don't know the history of the bike maintenance wise, except Castrol 20/50 was written in the owners manual.Since my bike was made in 1982, there has been alot of changes in motor oil of all types.I have used rotella t, delo 400, and now have delvac 1300 in it. It ran fine on all these oils with the exception of rotella, in which the shifting seemed a bit crunchy. It was alot better with Delo, But seems the best with Delvac.So being the oils of today are made better with better additive packages,it will keep these old bikes around for a long time.Even the old notion that you should change your oil before storage doesn't really hold water as alot of bike are stored for years without any noticeable damage.Then someone decides to bring it back to life for less then new bikes sell for. I'm sure mine was rolled into the garage and forgotten about for years as it only had 38k miles on it when I got it.Still it doesn't use any oil between changes, has any leaks or smoke, and hits the redline real fast.I noticed when I changed my starter a few months ago, it was perfectly clean in the motor, looked like new. I change my oil every 4-5 k miles or about once a year.With the detergents they put in oil these days it seems to handle the chore with no problems.In my owners manual they weren't real specific about which oil to use except for saying 10w40 or 20/50 when running in hot areas. I don't think there were motorcycle specific oils back when my bike was made.Bikes made today seem to be harder on oil especially the air cooled ones, so for those you need to be more vigilant in what you use and keep changes close to what the book calls for, as far as how the bike is run.,,