I have a 13 year PRV50 water heater that just started leaking thorugh the disdharge pipe and is filling up a 5 gallon pail in about 12 hours. Is this worthwhile to repair or simply time to replace unit

It is Temperature and Pressure Relieve valve that is leaking. It leaks because one of the two things is happening:

1. Water is too hot. Set thermostat to 125 F
2. Water pressure is too high. Measure your water pressure. Reduce pressure to about 55 Psi

However, you have to replace this leaking valve with new one.