See if i am thinking right. Looks like the tension adjustment pulley is in between the engine and the left pump. Maybe crank more tension in or if there is enough adjustment available, use a slightly longer belt for more belt wrap on the left pump?
No no seals inside the pump. You have two seals in this type pump one on the input shaft and one on the trunnion shaft. This the shaft the control arm goes on. There are some o'rings on the check valves and the relief valve.So there are no seals on the pistons or anywhere else inside the pump?