Cant be sure until you take it apart, but look at the compression pattern. The left bank is clearly higher than the right. When was the compression test done? Right after the belt was changed? You need make sure the belt is set exactly to the correct marks, and also count the teeth to make sure. Possible you have been running with it like this since the belt was replaced. Did you recheck the compression lately? Readings from a year ago dont really do you that much good in diagnosing a problem that just occurred, except for historical comparison.