Had the same pink pool in the foot well passenger side and matrix base of my 02 k. After removing the heater and testing it, (same as you do a tyre, sink in a bowl and use foot pump with a few home made adaptors pressurise,dont overdo it look, for bubbles ) I found no leaks. Turned out the leak came from the spiggot/ hose unions.The coolant finds its way back into the heater box. Clean paint and residue off the spiggots, bin the hose clips, replace with good quality jubilee clips ( other clips available, but not recomended). Job done. Fixed. Fingers crossed your is the same.