I dropped three tablets in this morning. I am not expecting this to be a long term fix, I am just trying to buy some time since I don't have time now to change the water pump but I will have time in about a month. Replacing the water pump on a diesel G-van is time consuming, takes twice as long as it does on most vehicles since many items have to be taken off- vacuum pump, alternator and its mounting bracket, timing cover etc.
Only reason I think a stop-leak might work is because, sometimes, water pumps leak after a flush of the cooling system. Don't know why it happens but it does. So, if the pump seal leaks because old deposits were flushed out, perhaps new deposits from a stop-leak might plug a seal leak.