It really doesn't matter if they were brand spankin new...........

The brakes were never designed to stop 7,000 lb. If any emergency occurs that requires stopping in any distance less than forever...........there's going to be a bad outcome.

I towed a 7,500 lb. horse trailer (with three horses aboard) with the B-250 (318, 3 speed auto) for 600 miles. The trailer had sufficient brakes...........but, I'll never do that again.

The situation with the W124 is far worse.