I recently discovered all sorts of soot/coal deposits over the engine block, and this was diagnosed to be a leaking injector seal, and I've had all 4 replaced.

What I've also noticed is oil in the large corrugated air filter hose, and also in the bent smaller hose that spurs off it. This smaller hose has a plastic clip connector (not a hose clip) at the rocker cover end which is near to an "oil cap" sized cover with a series of 6 clips holding it in. (Q1: What is this by the way) This hose's plastic connector does not fit particularly well it seems, so perhaps this was the cause of the mess on the engine in the first place, and not the injector seals?

Q2: How snugly does your hose fit to the rocker cover end? Mine seems fairly loose to me, but I was wondering is this normal?

The mechanic at the place that replaced the seals said oil in this hose and the air filter main hose is normal as it is acts as a breather to the rocker cover and the oil comes down the hose, into the main air filter hose and back into the turbo.
Q3: Is this correct? Seems like a lot of oil to me. Some has even contaminated the air filter itself.