Ok I’m stuck....

So for a while I had so lean codes and eventually these were fixed by changing the maf and all four o2 sensors a cat and a couple of leaky hoses.

Since then it has been running silky smooth but I occasionally get both banks running rich... checked the faults and I had two coils misfiring fairly regularly so I changed them and cylinder 8 as that’s a sh*t to do and I thought when in rome....

Anyway no misfires running great but still occasionally getting the same thing come up rich on both banks, tried a can of bg44k, new in tank fuel filter still occasionally coming up.

Last straw a smoke test and I pumped it in through the air intake after the maf so it would check the crank case and the air system and there was a leak at the bottom of the oil filler cap tube. It wasn’t massive but it was there... would this be enough to make it Chuck these lights on I assume it’s rich as it’s losing air that’s accounts for when under pressure?

If this still fails where’s next on my list? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

In case anyone sees this - changing the neck stopped my nasty rich faults  Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF