I have power into the heater and at the poles of the thermostat breaker not tripped and still rocks on and off solid

Turn off the breaker. Using an ohmmeter check the resistance of the element. If it is infinite the element is burned and it is time for a new element. Also these heaters have a safety to prevent overheating. It is a thermostatic switch. This may be the problem. Both of these items are available from Marley, but it may be cheaper and quicker to buy a new heater and take what you need from that,or replace the whole heater.