Bests & Worsts Reviews from Amazon

I have been using this product for seven years. I have liked them very much until recently. The last three brush heads, (sensitive), I have used have been horrible. The inside of the brush head handle grows black mold. I cannot figure out why. I use them the same way I always have. After each use I remove the brush head to let it air dry for 24 hours. Now that doesn't matter. Mold grows! So now I spray a Qtip with Lysol and swab out the inside. This doesn't last. Now, I tape up all the holes with duct tape. This helps but is ridiculous. What has happened? Anyone else experience this? I hope they fix it.