Before replacing a rack & pinion due to a fluid leak at the input (pinion) shaft seal, always diagnose why. An input shaft seal is not designed to have more than residual pressure. The pressure and flow is retained within the spool valve, unless higher pressure within the system is causing fluid to push beyond the spool valve and into the input shaft sealing area. It's a simple statement, but pressure will always follow the path of least resistance and eventually escape. In this case, please examine the steering system, in order to find and prevent a recurrence.
One potential root cause of residual high pressure can be a restriction in the return line due to rubber breakdown or internal collapse. This causes back-pressure to build up in the rack & pinion and an input seal leak. Replacing the return line will eliminate this problem. Also remember that restrictions in the return line can also cause noise, binding, hard steering, leakage and/or poor returnability.
Another root cause of input shaft leaks could be line reversal during installation. Many Ford applications have the same fitting size for both the pressure line and return line, so there is a chance that the pressure line was threaded into the return port and vice-versa. If this is done, and the vehicle started, the pressure will be directed through the top of the spool valve and out the input shaft seal. Once this mistake is made, the damage is already done and the unit must be replaced. In order to prevent this, clearly mark the original unit and lines, before removing the unit from the car. Use tags or differently colored paint pens, then transfer the tags or markings onto the replacement unit. The same application requires a check valve to be reinstalled in the pressure port of the replacement unit. So don’t send it back with the core. (See figure below).
A common mistake when a leak occurs is to tighten the lines. However, over-tightening will actually compound the problem by stripping the threads. Since most rack housings are made of aluminum, the soft housing threads will strip away against the steel threads of a fitting. CARDONE supplies new o-rings or Teflon rings with each unit, in order to provide new sealing materials versus using the old and distressed ones. So take the first step to avoid leaks, and always replace the o-rings or Teflon rings. Last, never use Teflon tape as an attempt to seal the fittings. Teflon has a tendency to cover the ports or unwind into the rack spool valve, causing the unit to fail.