headgasket? condensation? or just a leak??

L series 1999 80k miles-
So the new engines been in approx 3 months... Recently replaced all water hoses/pipes due to a leak (corrosion at bend on water rails) Anyway... I'm going through litres of coolant weekly, but no sign of a leak from where I've been parked.
This morning I filled it up again.. And checked my oil, and there's mayo on the oil cap.. Wiped it off and set off on my journey.. (couldn't get hold of my father to find out if i should be panicking or not) Runs fine- doesn't over heat.
I've just checked the coolant level again-bone dry (drove about 85miles after filling it up to max this morn) checked oil cap again... No mayo...
Now I've just been told by a friend who's a bit of a petrol head that it might have a leak from around the water pump (apparently common?) so I wouldn't notice if it was leaking as I'm driving.
Anybody have any ideas?
REALLY hope its not the h.g as then I'd be the only person to have a 2wd freelander that's snapped a cambelt and blown a h.g on a new lump in a matter of months!!!
DAMSEL IN DISTRESS

a pressure test may find the leak you can make up your own kit for free
a valve from a local tyre out let a spare expansion cap from a scrappy and make this oh you may have to spend a £1 for some silicon



then use a tyre pump take it tp 10-15psi


Ron

Will try that one!! Thanks very much

expansion tank is a known place for leaks , check for cracks in the plastic. Mayo in oil is not a good sign , i'd keep a check on that.
also check for leaks at the ird cooler