I find it odd that some of your fittings have two compression washers on them, one is the norm, I'm not understanding the need for two, did it come that way or did you take your spares from parts bag and double them up for some reason?
Yes, some have gotten away with standard synthetic oils. some have had the crank case cover blown completely too. As well as destroyed valves and rods. Just because some poster says he has gotten away with it, doesn't make it he smart, or correct thing to do. There are a lot of things you can get away with Sometimes, Some times not. Exactly where the game Russian Roulette comes from. I'n not playing. [size=78%] [/size]
My Yong Heng has single washers on the small dia line fittings and double washers on the larger tube fittings.