Biofilm purging -- the non-negotiable maintenance step
Monthly jet purging prevents biofilm buildup in the jet plumbing: fill tub 3" above jets, add 2 tablespoons of a low-foaming jetted tub cleaner (Oh Yuk, 2 Oh!, or Whirlpool branded cleaner), run jets for 15 minutes, drain, refill with clean water, run jets 5 minutes to rinse. Missing monthly purging is the primary cause of premature jet system failure and the source of black flake discharge that homeowners report after extended non-maintenance.
Jet nozzle replacement
Whirlpool jet nozzles thread into the jet body and can be replaced individually. Contact Whirlpool's bath division (separate from appliance support -- bath parts line) with model number for the correct nozzle part. Most nozzles unscrew counterclockwise by hand.