The 124 cars have a completely different heater control valve than the earlier cars with the monovalve. The valve seems to be quite trouble free and from what I can see is not made to be repaired, it is a discard and replace item.

If your valve is causing excessive heat, the problem is probably related to the controls for the valve, not the valve itself.

There is a very good article in the DIY section on this site that explains this subsystem.

Have a great day,