Mark,
On the rare occasion that you have a water pump failure on a 3126, the vast majority of the time it starts as a slight leak from the weep hole at the bottom of the water pump, it is rarely an emergency repair situation, and not something that you want to do beside the road when dealing with catching that much coolant. Since the water pump is readily available at any Cat dealer, and there is a Cat dealer in most large towns, I would recommend that you concentrate your limited spare parts inventory to higher failure rate items like blubs, alternators, belts, and filters.
Gerald
