I’m losing about a quart of oil every 200-300 miles. The underneath is dry with no visible leaks. Nothing around the engine anywhere. No blue smoke on start up, no blue smoke driving. Nothing…..
I’m now also losing about a cup of water from reservoir about every 300 miles. Again, no visible leaks, no dampness after she sits. No white smoke, no rough idle and no issues anywhere.

Complete mystery….. half afraid that this is the signs of an impending head gasket leaking…….

Thoughts?

Doubtful that it is a head gasket, the only time they cause an oil leak is when it dribbles out the outside and runs down the side of the block. Coolant from a head gasket leak will get into one of the cylinders. Waterways are only by the front and rear cylinders so the first place to look would be to see what state the spark plugs are in. Any looking steam cleaned compared with the others, could be the sign of a leak.

Both fluids have to be going somewhere. A slight coolant leak may not be visible if it evaporates from engine heat but may be seen as slight crystallisation of the anti freeze (or pink stains if you have OAT in it). That amount of oil must be going somewhere. How about at the bellhousing in case it is the rear main seal?

Must be going somewhere I'd guess rear seal and it's filling bellhousing as for water could be under expansion tank ---- possible head gasket starting to fall or small leak from heater matrix ---- lift carpets you'll soon know

if you think its burning oil just stand around the back of the car , if the fumes start to make your eyes sting , its possibly burning oil . as for the h2o disappearance when you drive somewhere just lift the bonnet and feel around for the hole under the water pump for a leak , they can be very discrete until its obvious.

Thanks for all the input…. I’ve checked everything as mentioned prior to making the post….
I’m going to have to put it down to global warming and continue to top ‘‘em up…..

Slight coolant loss - check the infamous intake heater for crystalline deposits below it on the rocker cover. They tend to leak when the coolant has heated up and pressurised and then drip coolant onto the hot rocker cover from which the coolant then evaporates leaving no liquid but the tell tale colourful dry crystalline deposits are left as evidence.

Oil loss - if the rear engine oil seal is leaking then the bell housing shouldn’t fill up as there is a drain hole at the bottom out of which the oil runs and then down the sump and drips off the sump plug (which can be misdiagnosed as a leaking sump plug). However if crud has accumulated in the drain hole then who knows? Perhaps check the drain is ‘clear’ of debris.

JCML, don't despair, you never know! Keep searching!

I've had a little loss since a long time, and I also gave it as "endemic RV8 issue", until I found that by pure chance that my 'top hose' has a weep, most wicked on its rear, towards the alternator pulley! Nearly impossible to see, I've discovered only because I was running my fingers through it seeing how to change the aux belt!
You never know ....

My oil also goes down, I've always suspected is burnt, but after the episode above I've run my hands (gloved!) through the entire engine and found out a 'weep' at the rear of the rocker gasket (where the coils are), and down the engine in the bellhousing. Better to leak than to burn, if you ask me ...
It is very relaxing and pleasant to "touch" your engine, has some sort of almost erotic thing to it ... lol

I invested in a cooling system pressure tester for investigating leaks. The one i have got is actually made in the States by Stant. I bought it on Amazon. It comes with its own pump and you also need to buy the right adapter to fit the reservoir (BMW).
It has proved really useful. Just pump up the system, from memory I think to around 10 psi, and leave it for a few hours to see if the system is tight.
Apart from the dreaded jubilee clips and perished hoses, I have found one of the main source of leaks is the reservoir itself. The caps wear and leak and eventually the plastic screw thread gets worn. I put a bit if silicone grease on the thread so the cap can be tightened down fully.
The level in my reservoir levels off around the top and bottom join in the plastic. Fill it any more and it will loose a bit before levelling out.
Can't help with the oil loss. I have got the diesel, which always blows smoke from the exhaust and drips oil !