FWIW: Just one set of experiences:
1. When the water pump packing is left with no lubrication, the packing & the shaft begins to wear in concentric rings at this joint when the engine is running, the wear causes a lose joint; hence, coolant begins to leak.
2. If one can move the worn water pump shaft fore & aft, more wear occurs as the fan moves forward & rearward with its concentric wear rings; however, Model A vendors sell a water pump shaft part to stop this fore & aft movement which greatly helps to reduce wear.
3. If one later adds lubrication, plus tightens the packing, plus stops the fore & aft movement, the softer packing will seal the worn concentric rings on the shaft & the pump will stop leaking.
4. The presence of water on the impeller cools the shaft, helps to keep the packing cool & prevents both the packing & shaft from expanding & creating a very tight joint while the engine is running.
5. If your water level gets very low, not lonely will your packing & shaft get hot, but they will wear very quickly when this joint tightens with expansion.
6. You may ask: How do you know this?
7. Over 50 years ago, as a teenager, prior to formal higher education, I installed a Model A water pump in a boat & used it as a stuffing box where the propeller shaft passes through the bottom of the boat.
8. With the boat engine running, the boat moving forward, the water would get sucked away from the upper dry propeller shaft entering the boat, & the packing nut would get very hot, expand & wear rapidly.
9. I learned from my Dad to loosen the packing nut while the engine was running to keep the upper shaft cooler, & tighten the packing nut about 1/8" of a turn when stopped to avoid leaking.
10. The moral of this story is two-fold:
a. If you keep your Model A packing lubricated, & correct fore & aft shaft movement, as stated above in many replies, an original Model A water pump will last a long time.
b. Also, if you put a Model a water pump in a boat, you can go to Europe & back several times if you keep the packing lubricated & loosen the packing nut while the propeller shaft is turning.
It is your water pump, you have a few very sincere opinions, & maybe you should do what makes "you" happy.