You should never use bolts in the rocker pedestals of any aluminum head. I snug the studs with a t-handle wrench. If you crank on the studs with a ratchet handle, they will poke through. The other style heads mentioned in this thread as examples...... Cleveland and BBC......neither have pressurized oil involved. That is a huge difference. The outer threads of the insert must be sealed, as well as the inside threads. That is why I mentioned an insert with a bottom in it, like Tom P's example of those smog plugs. I have fixed few heads by using an all-thread 5/8 fine thread B-7 material, and drilling and tapping the 3/8 inside it, with a sealed bottom.
It's a tough fix to have to pull the heads. Putting sealer in the top of the oiler hole can lead to plugging the oil to the whole shaft if silicone gets stuck in the stand. I hate that you have the problem.....just trying to give you sound advice. Your heads aren't totaled, but there is a near 100% chance that the oil will come past the insert on #3 and/or #6.