the first signs of the head gasket starting to fail, in most cases is coolant seeping from the head gasket on the exhaust side, or over heating or coolant loss..if coolant is getting in the oil the oil will go milky.. if it has a cracked head or gasket failure between cylinders it will miss a cylinder or 2 and will get worse when hot.. if its only when cold, the flat spot could be a vacc leak or the 02 sensor or coolant temp sensor,
giving the ecu getting false cold start reading and running lean??

who told you the gasket was failing??

i think it was on here it was ages ago when i first got the nf

ive ran the dash in troubleshooting mode and it reads coolant temps fine

my o2 sensor looks newish but it might be old i did clean the engine bay a month after getting the NF

oil isnt milky

when i first start the NF it automatically revs to 2k then drops only for like a short second if that means anything

there is a lil bit of oil around the bottom of the rocker cover on the exhaust side near the front but i might of missed it when i cleaned it

the nf is good on fuel i get roughly 600km out of a full tank in town

has plenty of power and responds in good time i doubt its running lean

no missing going on motor idles smooth and runs smooth

leads i didn't do them but it has top of the line top guns in it and they look pretty damn new and i haven't done sparks or Roda button or distributor cap

im not sure what a hego sensor is

HEGO sensor is your O2 sensor

The NF uses a coil pack so no rotor button or dizzy to worry about

Sounds like you getting good fuel economy out of her. Is it using any oil or water?

oil got replaced 1000kms ago when i got it hasn't used anything noticeable

water its used a little bit but just from water expanding and going out the overflow on the bottle