~~UPDATE~~ Pricey but a great ending, (estimate $1,700, final $2,016 including oil service and a few other things). As was pointed out, the airbox indeed did crack and was thus replaced, with the addition of a pop-off valve. But there was a fabulous cherry on top as a by-product to having this done: the oil-return line that is integrated in there above the engine was cracked and split,
which explains why I've been suffering with what we thought were multiple oil leaks, (and thus the addition of a fire extinguisher between the front seats -- just in case). Now, since completing the R/R for the airbox, new oil-return line, new oil sensor switch and a few other benies from my benevolent mechanic, I've put about 60 miles on the car with zero sign of smoke nor stench of burning oil. Sometimes in life, ya get lucky
Thanks to all of you who took interest in this issue (!)