Here is a longer update from the last month so...
The first point on my agenda was tearing into the engine bay to wrap my head around it, I've read and watched plenty online about these but nothing beats the real mccoy. From what I've read the things I wanted to check are: the turbo oiling system and the vacuum system. Checking how bad the CBU and oil in the intake was also on my list.
After pulling the engine cover, airbox and ducting it was pretty easy to inspect the turbo oiling system. It looks like the line from the engine to the distro block and the line from the distro block to the hp turbo have been replaced with AN line equivelants, just the lp turbo oem line remains, it looks a bit weepy around the rubber hose and seems to be leaking as the undertray has a decent puddle in it under the turbos, more on this later.
Getting further into it, pulling off the cowling, strut braces and rear engine cover there is easy access to all the intake manifold bolts. A few connectors, intake hose and nuts and bolts and the intake was off. Surprisingly the CBU isn't too bad, much better than I was expecting, definitely still in need of a good clean. Looks like there is plenty of oil getting throught the manifold seals and leaking down onto the engine, rocker cover gasket needs replacement too. A catchcan system is definitely on the cards to reduce the amount of oil getting through to the intake.
After putting it all back together this wrapped up the first little dive into the engine bay.
Another important item on the list was sorting out the paddle shifters. Who in their right mind decided that pulling on either would upshift and pushing on either would downshift? Anyways, simple fix, airbag out, swap some pins over and leave some disconnected. Now the left is downshift and right is upshift with pushing on the paddles not doing anything.
Onto the next saga, the turbo feed line. After some time I decided to look back into the oil leak on the exhaust side as I had cleaned the undertray and a large puddle had formed after only a week of driving. It looked like it was coming from the lp turbo oil feed line banjo where it connects to the distro block. After attempting to tighten this slightly I had that dreaded feeling of it getting loose again. It looks like whoever was here last had overtightened the banjo and stripped the thread in the distro block (it is only aluminium after all). There was lots of back and forth on this one before Dad and I reached the conclusion of cutting down the distro block to reveal the undamaged threads further down the block. The block was carefully chopped 5mm shorter with a hacksaw and was flattened smooth with a file mounted in the vice. The threads were then cleaned up with M10x1.0 tap and bottom tap (shoutout to Tony for lending and delivering these). Some new copper crush washers (suprisingly Mitre10 pulled through on these, at the end of the hardware aisle is a whole bunch of interesting hardware in draws, a good one to keep in mind) and everything was back together. After a week of driving it looks like the leak is sorted and the puddle hasn't returned yet.
After the last issue where the distro block had to be shortened the oil line down to the lp turbo was now slightly stretched and under some load so I ordered the fittings to replace it with AN straight away. Whitbread performance does aftermarket oil lines for the 335D so I copied their line routing and setup. Was pretty straightforward with some -3 PTFE line, 45deg -3 fittings and two -3 to washer seal adapters, one m10 and one m12. Although probably unnecessary I added some heat sleeving as it gets pretty hot on this side of the engine.