Crankcase pressure is sucked out due to being connected to the inlet system.

Put too much oil in and there's less room for the air to move around hence the pressure build up.

To give you an idea of how much pressure there is, we use vacuum pumps on race engines which gains more hp.

MG

I am going to check the PCV valve at the weekend, could you confirm that what I am looking for is the black circular valve on top and towards the back of the engine.

When you explain it like that it kind of makes sense. The pressure in crankcase is not constant but pulsing as pistons go up and down. If there is less room it cannot swallow pulses that good and peak pressure at the top of pulse is higher and lower at the bottom of pulse making greater difference in max and min pressure. I can see how this could effect seals. This would also have more effect with low number of cylinders and less with higher number of cylinders I guess.

I checked the oil level in mine today,and after 500 miles it seems the same so maybe the leak is not as bad as first feared.

I have had a quote of £300 +VAT all in to change the crankshaft seal, plus a little extra should the cambelt itself need to be replaced (Was changed 3K miles ago by same garage). I dont know how this compares to others.

If your crankshaft front seal is leaking, your timing belt will be saturated in oil. So if your timing belt was replaced even 300 miles ago, I'd still be replacing it.

It needs to come off anyway to replace the front seal, the extra cost will be the belt itself, not labor. I personally wouldn't be happy running an oily belt. If it busts teeth, the cost of salvation could be crippling, probably spell the end of your car, depending on what engine speed the belt failed at.

Good luck!

Still monitoring oil use, done 700 miles now and the dipstick has dropped something like 1/4 of a litre in that time.

I have checked and cleaned the PCV valve, there was a lot of carbon inside but it seemed to be working correctly.

I have also cleaned some of the oil off the engine undertray and from the bottom of the sump. I have no ramps, so removed the lower fog grills and reached in through there. Luckily my arms are quiet skinny so I could remove quiet a lot.

A decision will be taken on what to do with the car when we get back from our family holiday to the south of spain, and yes I am using the A8 to get to Estepona via Santander, finger crossed it will manage the 2.5K miles or so it will be doing during 3 weeks from mid June.

I now have an idea of how much oil its loosing and its not a lot really. The 8 has recently completed a trip to the Costa Del Sol and back, 2200 miles were covered in total. Today I checked over the car, and needed to add 1/2 litre of oil and a tiny quantity of coolant to the engine.