Back in the middle '70s, when STP came out with their "double filter" oil filter, I got one for the '66 Newport. Had been using normal Motorcraft FL-1A filters with no issues, but wanted "something better" (allegedly), so I got one.
At the next oil/filter change, we put it on. When I started the car, the oil light did not go out as it had been doing, but stayed on. No additional engine noises, just that the oil light would not go out. After a few minutes of that, it came off and a new FL-1A went back on. Oil light went out immediately, as it had been doing.
The suspicion was that the added filtration in the STP filter was a "resistance to flow", allowing some through, but not enough to turn the light off. Therefore, I might inquire as to what oil filter is on the engine?
At the time, the car had over 100K on the engine AND accumulated about 50K more afterward, when I got the '70 Monaco Brougham "N" as my daily car. The Newport began to lead a sheltered life under the carport.
Just some thoughts,
CBODY67