Some poeple clean them once a year, others twice a year.
But twice a decade? YES it will help. That soft rubber seal under your oil cap is no match for high crankcase pressure. It'll coat the whole engine in no time. And any other leaks you might have will be greatly reduced if thats not the culprit. (though I'll bet it is.) And when you've cleaned or replaced everything you should, don't forget to ream that little vaccum hose neck through with a drill bit of the proper size. Same deal on the intake manifold side. (or better yet replace the whole thing.) At high crankcase pressures, you can blow some pretty big and expensive seals. Hurry and do it. The 700/900 FAQ has the pics and info.