Code P0442 on 2007 Forester

I checked it out with my scanner and it says it's a small leak in EVAP system. This happened before about 10 months ago. I tried removing and reinstalling the gas cap to see if that worked---cleared the code and it's back again after all this time. Since this is only the second time, are there any simple things to check before going to a dealer? Thanks for all replies!!