oil leak 84' cb450

[matimus]

hello everyone, I just purchased my first bike, I had it into the mechanic to have it certified, which it passed, however after I rode it home I noticed some oil splatter on my jeans, I traced the leak to the bolt shown in the picture http://img.photobucket.com/albums/v2...y/DSC06187.jpg I checked the valve head and gasket which didnt appear to be leaking and was dry, the area around the bolt had oil on it, I left it sitting for the past few hours and there is no drips on the driveway.
The bolt itself is tight, can anyone help with this?

thanks in advance,
Matt.