DIAGNOSIS Probably not defective, just clogged. Mineral scale from hard water builds up inside the showerhead (where the water drips) and the internal tubes, messing up the water flow and temperature.
FIX You need to descale. Mix one part white vinegar to two parts water, fill the reservoir, and run a brew cycle without coffee. Stop halfway, let it sit for 30 minutes, then finish the cycle. Run 2-3 cycles with plain water afterward to rinse. This clears out the blockages.
IF THAT DIDN'T WORK Check the showerhead itself. Under the lid, there's a plastic piece with small holes. Use a toothpick or pin to gently clear any visible gunk or coffee grounds clogging those holes. Restricted flow there causes weak, uneven brewing.
HEADS UP Don't use harsh descaling chemicals like citric acid powder unless specifically says it's okay; they can damage internal rubber seals. Vinegar is the safe bet for this model.