Sounds like a left caliper is not doing much, most likely the front one.
Could be stuck, or could have air in the line.
Has it been sitting in storage recently?
Jack up the front, have someone apply the brakes, first very lightly, then progressively harder. Compare how much force is takes for you to turn each wheel. Any notable difference would prove there is braking problem.
This could actually be a steering or suspension problem.
Most roads have a crown which would enhance the odds of a suspension/steering problem causing a pull to the right.
Are your front tires wearing evenly?
1986 300E 5-Speed 240k mi.