Remove spark plugs and look in the cavities for oil.
You can hopefully get a finger inside to feel ev oil inside, like the upper part.
Oil can also weep from valve cover gasket if broken. The aftermarket gaskets have usually bad fitting between 2-3 at front. If tighten one of the M6 bolts holding the cover, gasket can or will snapp off. Bad fitting gaskets must be dressed with sharp model knife/ scissor to fit and all bolts have openings for their holes.
I have had an oily front between 2-3 and down due to the breader cover on valve cover. I had forgotten to tighten the front M6, so the o-ring did not seal.
I was surprised that oil weeped against the wind
If more like rubber pucks leaking...
An issue like this is not that big job on a CB750 with frame kit.
Off with valve cover, cam and holders.
Reseal the rubber pucks and check if cam holder studs have been removed. If they have, thread sealer is needed. High temp version.
When doing this retighten all head nuts. 20 ft lbs.
I tightened 20.6 ft lbs with stock studs and fiber gasket.
Lately with HD studs and MLS, 21-22 ft lbs.
