1988 Cadillac Brougham Oil Consumption

This vehicle has been in our family since new.
It has been consuming motor oil, 10W30 for some time but now it is using approximately 1 quart in 150 miles.
There is very little oil on the garage floor, and no evidence of colored smoke coming out of the tailpipe.
Please give me your suggestions on whether an additive or some other remedy would be practical.