Good news : the spark plug porcelain was cracked, and judging by the black dust on the installation end was letting air/fuel mixture through, which I believe was causing the forceful ejection of the spark plug boot. New plug resulted in immediately smoother revs throughout the range, and hopefully no more pop-offs. Bosch Super Plus plug was only 3,000 miles old. Odd.

Thanks for chiming in.

 

Nice job.
The air-to-oil mixture igniting would be an incredible phenomenon!