I was losing coolant ever SINCE i had my water pump checked (screaming engine after running hard). Apparently the dealership over torqued the plastic inlet flange thingy on the bottom of the engine when they replaced the pump (still have warranty, I didn't look I just lost coolant and complained).
Anyway.. lost small amounts of coolant for 10k miles, figured it was a leaky coolant tank cap, then all of a sudden lost the rest. Like.. big pool under the car, thank goodness for coolant reservoir sensor. Had it towed to dealer, and they found that that plastic attachment thingy had given up. When I asked how... they said "its plastic, these things happen" which is true I suppose. My mk1? or mk2? one of those, had the same type plastic inlet on the top of the engine and I lost 2 of those for unknown reasons... just noticed the left over gunk from the leaking coolant till it started dripping.
Anyway.... watch it.. smell for coolant. It doesn't just disappear.