Vandersteen is a good company all around, and the 5 is a very nice sounding speaker. One of a few multi-driver dynamic speakers that I can listen to for prolonged periods. It seems you've correctly identified the problem and were therefore smart enough not to blame it on the VPI, as so often happens.
Give and Take
I got the VPI 2nd pivot and installed it today.....you might ask my impressions.....What I did notice was a strange metallic sound coming from the midrange speaker of my Vandersteen 5A. They told me to remove it from the cabinet and send it to them, and they will rebuild it...so although the 2nd pivot is installed, I can't tell what it sounds like.