Lastest trip to a radiator shop said it was not leaking fluid and they want to flush the heater corDoes anyone ever have any one flush the heater core and how is done with taking the dashboard out ?

Yes the heater core is flushed by tapping into the heater lines under the hood of the car. It is usually done with an entire cooling system flush. It cleans out any gunk built up in the system, particularly the heater core so that the system can work more efficiently and so that fresh coolant can be added to the system. No removal of the dash or anything is required. If the heater core needed replaced, then that may be accessed from under the dash, but it sounds like you just need a flush.