[LPB]

Have you checked for a leaking heater core?

 

[LPB]

Is it bad to bleed air through the bleeder valve when the car has had a long and hot drive? I get lots of hot air when I do this - but this air just naturally occurs through compression doesnt it?

The cooling system is a closed system. You should not be continually bleeding air. Need to check for leaking hoses, radiator top tank crack, head gasket failing, and heater core leaking.

As mentioned the heater core will drip coolant into the footwell on the passenger side. Put your hand on the carpet and test for moisture. Will also leave oily residue on windshield. Touch with fingers.