98 beetle coolant problems

My 98 beetle always smells like coolant and every couple of weeks I have to add coolant mixture to the expansion tank because the red temp light comes on and beeps. It is not leaking and I had the flange, the fan and some sensors fixed a few months ago. I notice that the cap on the tank does not make a locking noise like it used to, so could that just need replaced to get a tighter seal? Also, because it is still cold in Utah, when I run the heater in the morning, it gets hot until I have to stop at a light or stop sign, then the heater blows out cold air. Is it the heater core and how hard/expensive is this to change?

water pump 99% sure

Thanks. I know a reputable local garage (not a dealer) that only works on VW's and they do free diagnostics.

Make sure you get a second quote...free diagnostics is a good money earner!

water pump 1000% sure