Well some people have mixed Xylene straight with 93. It's one of those things, without a scientist and controlled testing over time, it would be very hard to tell the effects. But I play it safe and use a lubricating oil, they say to use either ATF or Marvel Mystery Oil, the M.M.O. was about 3 bucks and it is designed to go in your fuel (unlike ATF) so I felt better going with that. I think I use 2 or 4 oz per 5 gallon of Xylene (and 15 gal of 93). The Marvel Mystery Oil is in a red bottle with black label, and the Xylene can be bought at good paint shops like Sherwin-Williams. Expect to pay about 5 or 6 dollars a gallon but it still is cheaper than paying for a tank of 100 octane Unleaded racing fuel.
Toulene can also be used in place of Xylene but I found it had a slightly lower octane rating and it was a bit more expensive, and less popular.