[greg64]

One thought that occurred to me... You mentioned that the calipers were changed by the PO. I've had experiences over the years where the wrong caliper was in the correct box. There are a number of calipers with different piston bores that have the same mounting ears. Maybe your two front calipers aren't matched, leading to the left side being weaker.

Also, make sure the front flex lines are in good condition. I've had problems before because the inside of the line had collapsed.

Good luck!