Think I just answered my own question. Not much on the internet about the stuff, but found this on a Yamaha discussion forum:
"I'm assuming you mean "graphite". Remember Arco Graphite oil? If you don't there's a good reason for it. They put larger amounts of graphite in this oil which would end up in your oil pan. After many changes of this oil, you would end up with a pan full of it. Lost my '79 Chevy pickup truck motor to it. Took off the oil pan and it was about an inch thick in the bottom.
The oil sump was plugged with it also. Not such a good idea."
I'll stop wondering about it now I guess
