Having owned both at the same time, I have no problem saying that the M91ED is a superior product to the M97xE in just about all areas.
I have no idea why but I can say that the former is the V15 type 2 in a slightly different body and that it has a nude mounted elliptical stylus as opposed to the bonded elliptical on the M97xE.
What you are seeing is the adhesive breaking down. You can try to correct the problem by carefully adding the adhesive of your choice, or buying one of the many available M91s on Ebay.
I have no idea why but I can say that the former is the V15 type 2 in a slightly different body and that it has a nude mounted elliptical stylus as opposed to the bonded elliptical on the M97xE.
What you are seeing is the adhesive breaking down. You can try to correct the problem by carefully adding the adhesive of your choice, or buying one of the many available M91s on Ebay.

