Demagnetized pole piece???

Hi all,

I posted before about this, but I've since got some more info:

My D-string has very low volume on the bridge pickup of my P/J Tune bass. It's fine on the neck, and the bass is setup fine.

After some investigating, I'm thinking that the pole piece below the D-string has become demagnetized. Symptoms:

1. Tapping on pickup with hex wrench yields no sound under D-string.

2. Field under D-string repells hex wrench. Under all other strings, wrench is attracted.

Anyone heard of such a thing happening? The pups are non-adjustable, and potted. I think I'll need to buy a new one