globalmaa;
As you see in my picture, there is a gasket, an O-ring, and an oil seal. When you replaced the camchain did you replace any of these? If those parts are old, they may need to be replaced.
Its important that the camshaft is centred in the engine, and its also imporatnt that the camshaft bearings were placed fully inward toward the centre of the engine.
You should measure both ends of the camshaft that protrude past the bearings. You want to have an equal amount on both ends.
You could remove the housing and polish up the surface of the camshaft, so that the oil seal lips have a nice clean surface to mate with.