I don't think taking a jug off is that difficult and I'm no engine guru at all. 4 bolts and carefully slip it off being carefull to not tear the gasket (should really replace the gasket anyway). You may have a stuck ring. You can clean it up and probably unstick the ring if that't the problem. Maybe a bearing is worn out causing the RPM drop. Lots of things can cause loss of power. Just make sure to take note how it comes apart so you can put it back together correctly. Especially if you take the piston off the con rod.