I don't have the answer to your problem as I retired in 1991 so I have no absolute knowledge of your PTT unit. However, this will get your post back to the top of the list... plus a suggestion (below).
You need a colored diagram of both the up and down fluid flow, normally included in a factory service manual specifically for the engine you have... NOT a manual that covers a half different models which is quite confusing.
By studying the diagrams, one can normally see what valve(s) should be closed and might be leaking when pressure is applied to it via the reverse mode.