Engine 16hp walker mower Valve Covers

I have a low hour (< 300) 16hp walker mower that has been well taken care of. However recently it has started to backfire when I shut it off. Looking at the engine, it seems that I'm getting an oil leak from one of the valve covers. Can I assume that this just needs a new gasket? Is it relatively easy to do this job?

Last ... would a leaking valve cover explain all of the following symptoms:
- an oil fouled spark plug just below the valve cover
- backfiring when the engine shuts off
- engine misfiring while mowing (but not so much just driving)

Thanks

Engine 16hp walker mower Valve Covers