I'm not a tech but if you are certain it is this area that is leaking oil then consider changing the gaskets (part #6 and 17) in the diagram. I believe part #6 may have a filter and you could just clean it as debris can clog it and cause issues and maybe the leaking oil. If it is clogged, replace oil and filter. You have been getting regular interval oil changes haven't you? You can also check the valve itself by measuring the resistance and the valve itself for movement. Lastly check the engine oil pressure.