Just purchased an '87, (one owner bike) the guy used Gastrol GTX 20W50 all of the time and changed it every 3k. I called the local dealer to schedule a tune-up/oil change etc... and asked if they used Gastrol oil. He said they NEVER put car oil into a motorcycle and wouldn't recommend it at all. He said I should be using the Yamaha oil and that is what they generally use. The guy I bought it from drove it for 21 years using Gastrol - and everything seems to run fine.
Should I switch to the Yamaha brand?
I didn't think this would cause that much problem.
Any advice on this would be greatly appreciated!!!