Shimano GRX RX 815 Series Dealer's Manual page 152

MAINTENANCE
SHIMANO genuine mineral oil replacement
6.
Inject oil from the brake caliper side.
(1) Place a 7 mm socket wrench in the position shown in the figure.
(2) Fill a syringe with oil, and then connect the tube to the bleed nipple.
* Fix the tube with a tube holder so that it does not come loose.
(3) Loosen the bleed nipple by 1/8 of a turn.
(4) Push the piston of the syringe to add the oil.
(5) Oil will start to come out from the oil funnel. Continue adding the oil until there are
no more air bubbles in the oil that is coming out.
Bleed nipple
Tube holder
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