What is this leak?

[Steve Tinker]

The usual culprit of oil on the outside of the intake tube is from the hydraulic steering fluid overflow pipe - that's the reservoir located just behind the intake @ 11 o'clock in your photo.
Check the level and only use Pentosin CHF11S or CHF202 hydraulic oil to top up.

Oil in the inside of the intake tube can mean a failing AOS - check for oil again in say a thousand miles. Can you remove the oil fill cap OK with the engine hot & idling - a failing AOS causes a vacuum making the cap (sometimes) difficult to remove.....

[bcinphx]

I have CHF 7.1. I wonder if that's the same as what you're recommending or if it can be used. This is what I have from my BMW. Oil cap removal it's no problem so I hope the AOS is not malfunctioning (haven't noticed any oil from around the aos) but I'm still curious as to why there's oil inside of it - there are two vacuum hoses that I need to find out where they come from. Noticed a little smoke at startup lately. Probably from the oil in the intake tube. (Wonder why there is no oil in the lower tube). The intake tube has no cracks or holes and all four clamps are holding well.

[bcinphx]

I have CHF 7.1. I wonder if that's the same as what you're recommending or if it can be used. This is what I have from my BMW. Oil cap removal it's no problem so I hope the AOS is not malfunctioning but I'm still curious as to why there's oil inside of it - there are two vacuum hoses that I need to find out where they come from. Noticed a little smoke at startup lately. Probably from the oil in the intake tube. The intake tube has no cracks or holes and all four clamps are holding well.