"a leak in the valve area"
I assume you mean the "controller"? Per parts vendors these controllers rarely fail. It's usually an incorrect fitting of hydraulic line. Same for PS/SLS pump in that they rarely fail.

The system is "self purging" of air, however, if you've done any any major R&R, the fittings must be attached correctly. You may have to purge at the controller. An extra liter of FEBI 2615 fluid may be needed to adequately purge the system. This is not PS fluid, you must use 2615.

PS I'm not a maniac, however, I've been down this road with my 94 wagon and it took a few bleeds to get it right.