K4050 Retainer, O-rings, Seat

The water supply valves need not be shut off to make this repair but do NOT open the mixer valve until the repair is complete!

Remove long set screw - 2.5mm hex key
Remove short set screw (if applicable) - 2.5mm hex key
Pull spout straight up to remove - caution: water will drain from base of spout
Remove seat, O-rings and retainer - seat may have been left in faucet body
Clean spout and faucet body
Apply NSF-61 certified silicone (plumber's) grease to all grooves in spout base, inside surface of faucet body and inside surfaces of seat, O-rings and retainer.
Place seat, O-rings and retainer onto spout base as shown.
Apply silicone grease to outside surfaces of seat, O-rings and retainer.

Rotate spout until cross-hole in retainer is aligned with cross-hole in faucet body.
Lower spout into faucet body, without rotating, until fully seated.
VERY IMPORTANT- Use hex key to probe and verify cross-holes are aligned. Now you can rotate the spout while pressing with the hex key to 'feel' the hex key against the spout to confirm the holes are aligned.
Screw long set screw M5x0.8x7 into faucet body until seated against spout - CAUTION: set screw MUST pass through cross-hole in retainer and make contact with spout. Otherwise, water pressure will force the spout out of the faucet body when faucet is in use!
Rotate long set screw 1/2 turn counter-clockwise.
Screw short set screw M5x0.8x3 into faucet body (if applicable) until firmly seated against long set screw