HP LJ 2420 Gear Kit P/N KIT-24xx-GR-NN

The kit consists of three gears:

1) Narrow, rearmost 19t gear P/N RU5-0379.

2) Wide, upper-frontmost 21t gear P/N RU5-0377.

3) Lower-frontmost 20t gear P/N RU5-0378.

Item '3)' is the one that leads a hard life and wears out, making for a noisy gear train.

Each gear is held on its spindle by a claw -- they're easily removed. Replace all three. Grease the teeth. Lubricate the spindles with WD-40.