Thanks for both inputs. I'm sure the same pattern has been seen before, so unless one tells it is a definite precursor of a sudden catastrophy, I can live with the "problem" , not serious enough as to want working to eliminate the cause, as long as it does not worsen and will not cause to be stranded in the middle of nowhere....
...my cars have always brought me back home...even to jump a 3rd tooth of the timing gear ('68 Galaxy), or fry the ignition ('79 Country Squire) , or break the last strand of a corroded PCM supply wire ('87 Taurus), shoot the ignition module ('93 TS) ...etc.... just as I arrive in the backyard...