I can't help you personally since I don't have hydraulic steering on my boat to even trace the likely location for you. However, the folks at Wagner Wagner Steering - Hydaulic Steering
should be able to point you in the right direction--they may have a schematic of a typical system or even a customer file on your particular boat's system.
Their contact information is here Wagner Steering - Contact Us
There is a Corbin 39 owners group and many technical questions about the steering system have been posed and discussed here: http://corbin39.com/questionsandanswers.html
We hope you enjoy the forums here