We don't know "crossover" from where? and we don't know if flow is in or out of the hollow bolt. We don't even know if the hollow bolt has anything to do with the pump. Someone has to know what this is. I have searched the internet quite a bit looking for wording and pictures. Nothing yet except the repair manual verbage and the fact that one vendor sells two dual action vacuum wiper pumps, a 52-57 and a 58-62. A design change.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn