2006 Toyota Camry AC and Rack and pinion

If that cap is on the service port, just screw it on tighter. The valves in those ports commonly leak, but their job is simply to hold the refrigerant in while you're disconnecting the service hoses and screwing the caps on. There's a rubber o-ring seal in each cap to make the permanent seal that stops the leaking.

Replacing a rack and pinion assembly is not a do-it-yourselfer job. Start by getting a copy of the manufacturer's service manual, then read through the pages of instructions to see if you want to tackle it. If you do, come back here before you start taking things apart.