I absolutely agree with Coleighf. A problem like this will not cure itself and the more you use it this way the worse it will get and potentially cause further damage.
Just replacing the head gasket is obviously more straight forward than doing the valve stem seals as well but that is your choice. If it was me I would just replace the head gasket as I strongly feel that will be your problem BUT be aware that if the valve seals do need doing the head will have to come off again. Replacing the valve stem seals is more specialised and the valves need to be removed which does require specialised tooling.
I can supply you with a top end gasket set that covers all gaskets and O rings from the cylinder base gasket upwards but sadly does not include the valve stem seals. I can help you with those as well should you decide to do them.
Another area that could also cause an oil leak in that area is where the rev counter cable fastens to the head. There is an oil seal in there that does leak on occasions. this will tend to leak on the right hand downpipe.
Let me know what you want to do.