DIAGNOSIS Toothpaste, saliva, and water residue accumulate in the small crevice around the drive shaft, creating a visible ring of gunk.
FIX Unplug the charger. Remove the brush head. Use a dry, stiff-bristled brush (like a clean, old manual toothbrush) to scrub around the metal pin and the black rubber seal. Do this weekly.
IF THAT DIDN'T WORK For hardened deposits, dampen the cleaning brush with a 50/50 mix of water and white vinegar. Scrub, then immediately wipe and dry the area thoroughly with a cotton swab. Never submerge the handle.
HEADS UP Never use pins, needles, or metal objects to pick at the seal. You will puncture the waterproof membrane and kill the handle. The rubber seal is delicate.