which klotz are you using? i'm looking at some of their stuff and alot of it contains Tetraethyl Lead OSHA PEL (copied from klotz web page msds), (common in racing fuel) which is what used to be in leaded fuel which was phased out because it clogged cats.

i still cannot find negative's about toluene. in fact it burns into co2 and h2o. i don't know how that hurts the engine. also its natural occuring in crude oil and the manufacturing of fuel. alot of octane booster contains toluene. if you read uses and tech sheets, the first listed use is in fuel for combustion engine. it is used as a paint thinner, but i wouldn't say thats what it is. the paint supply store is mearly the easiest way to get it.