While the old valve is repairable, there is such a thing as life expectancy, and if you are putting in a tile job with a 30 year life expectancy, do you want to leave a valve body that is maybe more than half way there already??
The moentrol valve is still available. Another very good choice would be a Delta in the 1700 series. The 1300 series Delta does not give you separate control of volume and temperature.