The Wilwood 330-16239 is a replacement cap for Girling-style master cylinders and remote reservoirs. It uses a vented diaphragm gasket-style seal and is molded from durable nylon. Because it is sold as a direct replacement, it lets you restore a cracked or leaking reservoir lid on a Wilwood remote setup without replacing the whole reservoir. Owners on user forums say remote reservoir seals can be finicky, so a correct-fitting, properly vented cap matters more than it might seem. For a remote-reservoir brake or clutch build, a good cap helps the system breathe and seal under track-day heat. Search terms this cap matches include Girling-style remote reservoir cap, Wilwood 1.71/1.84-7 TPI reservoir cap, and vented diaphragm master cylinder cap.
Fitment is the key buying question. The manufacturer's side-mount short remote master cylinder install sheet lists P/N 330-16239 as the cap for that kit and notes it fits both reservoir sizes offered. Before installing, the manufacturer's bench-bleed procedure calls for plugging the outlet fitting, removing the reservoir cap, bench bleeding and filling the master cylinder, then installing it on the chassis. Once the system is bled, fill the reservoir to the max line and replace the cap, then test the master cylinder before use. Use the Wilwood brake fluid the manufacturer recommends for racing use. Owners on user forums advise lubricating the reservoir neck and O-ring with fresh brake fluid and avoiding over-torquing the cap, which can strip the plastic threads.
The manufacturer's install sheet for the side-mount short remote master cylinder kit lists P/N 330-16239 as the cap and states it fits both reservoir sizes shown in that kit.
The manufacturer's catalog describes the cap with DOT 3 fluid markings, while the manufacturer's shop lists it for use with DOT 3 or DOT 4 fluid from a sealed container. Details vary, so confirm the approved fluid with the manufacturer before use.
Per the manufacturer's remote master cylinder install sheets, this is a bench-and-bleed job rather than a bolt-on part, so it suits a builder comfortable with hydraulic work. Plug the outlet fitting before you pull the reservoir cap so fluid does not drain or contaminate the system, then bench bleed the master cylinder before it goes on the chassis. Common gotchas reported by owners on user forums include a reservoir that weeps at the neck, which is usually fixed by lubricating the seal with brake fluid and tightening only until snug. Check the fluid level at the max line once the brakes are bled, and test the pedal before driving.
