I would give Rich Verano, The YS importer a call. He really knows the engines and may be able to help with the gaskets (there have been after market gaskets available in the past, though I haven't seen an ad in the K-Factor for them in several years. Since the DZs use a different fuel delivery system, demand for quality gaskets (in the pattern market) has significantly diminished. You might try your local 'speed' shop or check online. I also remember seeing an ad for laser cut gaskets somewhere.
Good Luck. YS engines are great when they run right, but can be a PITA when you are chasing a problem...