My 12-year old Navtec began to fail to hold the air pressure, but was not leaking oil. If you go online, all the forums say they have to be rebuilt. Well, not yet. A West Marine hydraulics technician was kind enough to offer this possible solution:
If you have a Navtec backstay adjuster, you know there is a release valve on the bottom. It's turned counter-clockwise to release air pressure and clockwise to close the valve. The Navtec instructions emphatically state the knob should not be closed firmly, just gently.
Here is a possible fix--temporary?--if your adjuster looses pressure during the day. On the face of the release knob there are three small threaded holes, one of which has a set-screw in it. This set-screw limits the travel of the knob so it can't be over-tightened. The tech said to loosen this set-screw just a fraction (a half turn to start, more if needed), which will allow the knob to close more tightly. This is a trial-and-error process, so be patient.