firstly , im glad to see that there is still some activity here, im about to spend the morning going through the forum.
here is my issue and a brief backstory for context.
2004 k74

ive recently noticed an oily film in the coolant bottle
this is after a 400 odd mile round trip. on said trip i did briefly notice the chinesium auxillary temp guage register a drop in operating temp, down to about 70. only for a very short time.
once home and a couple of days after checked and it had gulped a wee bit out of the coolant bottle. maybe a couple of cm worth.
Everything was normal on the pre "will it make it round the trip" checks.

It was then given a combustion gas sniff test. this was fine. i decided to go straight to the worst case hahahaha.
its not lost any fluids since
there doesnt seem to be coolant in the oil. there is no overheating and the exhaust is normal, no smoke.
a short 20mile trip at the weekend there and it smelled hot when parked, like, hot enough to poke my nose under the bonnet. and i think the oily film is getting heavier.
Ive been all modern and trendy and asked the Facebooks for opinions.

it still has its egr and cooler, id have thought a fine sniff test would rule this out.
my logic would say that if oil is getting into the coolant but not the converse then its either where oil pressure is higher than coolant
Where might this be ?
Or
has the head or gasket gone between a coolant and oil passage but the combustion gases are still holding, hence the ok sniff test.
Is this a possibility.
well done if youve got this far. thanks for reading