The oil clips will surely help greatly. But warm the engine up first thoroughly and install them as hot as you can. You will still get oil out; it's time dependent. Are you using a high lift cam with this valve train? I think probably not as you would have more damage. Stock rockers have limited slot length and will bind on the rocker studs quickly beyond stock lifts, scoring and breaking studs and galling the valve stem tops. Make sure the rocker slots are adequate for your cam.

Otherwise your theory of a sticking lifter seems plausible to me.

Bummer dude ..........

Good Luck, Kitz