Did you use the RTV recipe specified, thats compatable with engine oil & did you install the covers while it was still wet, so that it could conform to both surfaces????

Was the oil leak in the same general area as the silicone & or the machine marks????
Did the oil leak come about suddenly after some event, or slowly over time???

Is the PCV valve due for a change & have you changed it??? If its sticking closed, it'll cause excessive pressure that can pop the weakest link in our oiling system seals.

BTW, the top end looks nice & clean of deposits. Be sure to use a shop vac to remove any remaining sanding or metal debris, before buttoning things up & let us know how it goes.