Burned valves have been mentioned here. Several weeks have elapsed between the fest an last incident. The car ran great and smooth. If it were a burned valve wouldn’t it have caused the first explosion and wouldn’t I have noticed a burned valve after I replaced the blown manifold the first time?
what about the purge valve sticking?
You've given little info on the car, how you would have seen a burnt valve I cannot imagine. Something ignites the fuel and the only thing I can think of is the combustion chamber leak.
Good luck.