I limped the 2 mile journey home and had a closer look.
Looking in the engine bay quite quickly yielded the problem, there was a fairly substantial amount of oil leaking from a couple of the hoses connecting to the power steering fluid reservoir.
If there is a leak, the oil level was obviously going to be lower than it should be. Taking a look it's not instantly obvious where the oil level should be, turns out on the underside of the screw cap is a sort of dip stick, with two marks on it. As mine wasn't even touching the cap's dip stick it was obviously quite low.
I topped up the oil promptly with Comma PSF, then set about ordering replacement hoses. Turns out no where sells these hoses except BMW. Expecting a large figure I called up and got a quote, however, not expecting the £140+ quote I received I reluctantly placed the order. I also went and picked up a couple of bottles of Comma PSF, as the bottle I used in emergency was an old left over bottle just to tide me over.
A quick peak under the car after getting it on the ramps ready to start the job, the under-tray started trickling oil...
The engine bay under those hoses was all covered in oil, even as far back as the control arm, so before any work continued it was all mopped up and cleaned as best I could.
I decided it would be best to remove the lowest point first and drain the oil out from underneath the car, this would ensure no more oil was leaked into the engine bay. That meant cracking and removing the bolt into steering rack. The bolt is a fairly hefty one, needing a 22mm socket to remove it. Ready with a container and funnel I cracked the bolt and drained as much oil as possible.
Draining the oil turned out the be the easiest part of the job, removing the other 'quick' release end of the hoses turned out to be a 2 hour struggle. I'm not sure in which dimension they are quick to release but they certainly wouldn't budge during this job. After many attempts they did come off, but not before some choice words were spoken, trim removed and a hack saw was taken to the one of the hoses to aid manoeuvrability.
To help access the air duct was removed in front of the fuel radiator.
With that out the way, the hose from the reservoir to radiator came off 'easier', here's the comparison old vs new.
Next was the hose from radiator to steering rack, this one was the real stubborn one that required hacksawing.
The reason why it was so hard to get off became apparent upon looking inside the hose, two of the prongs had come out of place and would have been stopping the connector come off.
Time to rebuild, first job was to find a replacement for the clip that was cut off the hose at the reservoir end, a 13-20mm jubilee clip did the job.
Next both hoses got connected to the radiator and the banjo bolt replaced in the steering rack.
The last thing to do was to fill up the reservoir and bleed the system. I found the suggested two turns full lock left and right not enough to fully bleed the system, it was more like 5 or 6. The level was topped up for a final time up to the correct level according to the dip stick and the job was complete.
Touch wood, there have been no more leaks as yet so a job well done.