Sounds to me like you have air trapped in the system. When it was replenished, did they have the heater turned on fully? I'm very surprised to hear that you are still getting coolant coming from the cap - considering the OEM cap is supposed to have 2.0 bar pressure... I suggest ensuring the heater is turned on fully, get engine to operating temp and bleed the air out via the screw on the tank. My system has never leaked and the float indicator is quite low in the tank (I can push it with my finger and it moves a little but is no where near the top of the tank).

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08/06 build 4.4i Stirling Grey over black