stt steering problem

I have a STT 61V-27KA that has a reversing problem on the left side. Some times it is hesitant or finally engages very slowley, or not at all. It's a problem sometimes turning left. I took it apart, and the only thing I saw out of order was the bearing insert in the back of the housing, which was loose but fit back in place very easily. Going forward is strong on both sides, and reverse is strong on the right, but the left reverse puts a small load on the engine, then drops off. Seems like I may have a bypass problem or some pressure valve is giving up too soon. Thanks for any suggestions--Ray