valve cover

I don't mind an oil leak on an old machine, but not on a brand new E110 with 3 hours on it. I mind very much when the leak is from the valve covers and the oil drips directly onto the muffler, causing a very smoky condition and the potential for a fire soon after you start it. I was curious...

I need to remove the rocker arm cover and our dealer implies you have to pull the fuel tank - the manual does not say that but says to pull the muffler.... from looking at the engine I think neither need be done to adjust valve lash - has anyone done this job and if so what do you suggest.

My 425 AWS with Kaw 20hp motor has a slight oil leak from a valve cover. I snugged up the bolts but they were not really loose. Does anyone know what type of gasket is used on these valve covers and if John Deere sells them individually?