Check the manual, but I think these are okay to run on 95 but running it on 98 super-unleaded will be fine. You don't need to use an additive to flush the engine as most good quality super-unleaded fuels contain something similar. If you're experiencing a flat spot under acceleration, then a few tanks of super should help clean things up. They were never the most economical cars in the world, so if you're looking to get the best fuel consumption make sure the servicing is up to date with fresh oil, filter, plugs and leads. These are great old buses that will soldier on for many hundreds of miles if they're well looked after. Enjoy!