Generally the issues that you are experiencing are caused by worn keys.  A code cut key cut correctly....not a duplicate...will go a long way in solving those issues.  Filing the wafers as suggested might work, but it does compromise the lock and doesn't really address the issue.  Very seldom do we see Vanagon locks worn to the point of not working correctly.  It's almost always a key issue.  We've had probably a half dozen just in then last week that were solved that way.
Steve Sandlin, Regsitered Locksmith