If that's a CB250RS, Yep, that oil leak sounds about right, mine does it too. The cambox/cylinder head joint is a metal to metal fit with no gasket. I've had a couple of attempts to stop mine 'sweating' using different compounds which have worked for a while and then thrown the towel in. I suppose that refacing the joint surfaces would help to stop the problem but then it would also reduce the bearing clearance for the camshaft that runs directly in the head so not such a good idea. When I bought mine for fifty quid ten years ago some herbert had had a bash of stopping the leak by using Isopon body filler over the outside of the joint, that didn't work either. If the leak isn't too embarrassing do what I do, wipe it with a bit of kitchen-roll every weekend !. Best of luck.