Dear Shades, to be effective as a tool for making JW's question their beliefs, any brochure/tract would need to be very short and succinct. JW's do not read large blocks of text, and have difficulty following an argument. They are too lazy to look up quoted scriptures.
A quote from their own WT publications showing that they (the WT) do not believe Jesus is mediator for the "Great Crowd of Other Sheep" (from the article in "Insight..." fer example) folowed by a scripture from Timothy say, to show that Christ is mediator for all men, then your question "Who is YOUR mediator ?" should be just enough, any more than that and they will simply toss it as "Apostate material" because it has a lot of text.
Just add a link to JWFacts.com and the relevant article therein.