I bought an 89 Lincoln Mark VII LSC with 5.0 HO in the
mid 90's - it had 105k on it then and had not been babied.
I switched to Mobil 1 a few months later after reading
I now have 218k on the car and it's still running good -
uses normally not over 1/2 quart to 2500 mi oil change.
Have a little seepage at the front seal and valve covers,
but nothing unusual.
I've driven it fairly hard with lots of long 80+mph trips,
mixed with fairly cold weather 20 mile trips and 90 deg
plus summer driving with no problems.
I use 10W30 and do not have any oil pressure problems.
With the overdrive trans
in cars now you don't run as
many rpms per mile so they don't wear as fast as they
used to, plus engines are built better and with better
quality parts, so wear is not as great at 100k as it was
not too many years ago. Besides, you're wasting
several horsepower and a little gas mileage pumping
heavier weight oil and it's harder on the distributor
gear and cam gear.