I have a 1998 A4 1.8T Quattro, when i bought it the heater blew cold air. The temp gauge always reads cold etc. I put a new thermostat and voila! hot air and everything was great. Well now just in time for upcoming fall and winter my heater is blowing cold with slightly less than luke warm at best. I tried every vent incase the doors werent operating properly as well. The cars temp gauge reads straight up (dead center normal operating temp) My only guess is the heater core is blocked/plugged since i am not losing any coolant. The hoses are hot, the coolant is definetly cycling, and i have a new water pump. OK on to my question. Would anyone suggest having a shop flush the heater core before just replacing it? The audi dealership service department estimated around $1200 to replace a heater core, that was just labor, so not including the 250ish for a heater core itself. I am capable of doing my own spark plugs, oil, air filters, cabin filter, etc etc but i have never attempted removing my entire dash board and such. I went all last winter with no heat and we had an insane snow storm up here that lasted weeks and the cold temperatures even longer, at best my car got to 40 degrees inside, i dont want to deal with that again. Any suggestions? Sorry for the long post but i feel in order to get good help my problem needs to be clearly stated. Thanks again

-Justin