Is it head gasket failure

my car has been losing water since i bought it not a lot but needs topping up every 2 weeks.

i have changed the inlet manifold gasket and cleaned the coolant tank out . last week fitted a new radiator and re cleaned the coolant tank out again as i noticed gunge on the side walls of the coolant tank, while the radiator was out i noticed a bit of mayo in the water pipe so gave it a quick wipe out. today noticed the gunge again on the side wall of the coolant tank.

the car runs fine doest not stutter

the heater blows really hot

no mayo under the oil filler cap or in the oil . the oil itself is clean

checked all under the car for leaks even left cardboard under it to spot any leaks nothing

checked driver and passenger foot well for dampness all dry.

is it the start of head gasket failure or is the mayo from previous h g failure ?

where could i be losing the coolant ?

i dont mind taking the head off and renewing the head gasket, but doing so it could mean unnecessary work i.e head skim

any advice please

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