So I've been using supertech full synthetic 5w30 in my 98cc flathead. Its ok, but it gets extremely dirty after a couple weeks. I put about 30-45 mi/wk on my bike, so I'm not sure if that's normal or not. Needed more oil and wanted to switch, was at walmart today and saw Royal Purple and grabbed a quart to try. Will it be worth it? Better than supertech (walmart store brand)?