hmmm is there mayo on the underside of the oil filler cap?
Does the coolant smell of petrol?
You need to do a compression test on all 4 cylinders to be able to rule out the HG going, you might be lucky and they havent - if you keep taking it out and thrashing it then you will only increase the chances of damaging the HG.
ignore what the previous owner told you had been done / replaced - start by replacing the coolant as the fact the bottom ones are warm not hot could signify a airlock. If this doesnt work then look at replacing the thermostat and take it from there (cheapest first)