Engine Malfuction, New Cats, Blown Turbo?

[Florida E70]

Hopefully someone can shed some light on my 2012 E70 35d's problems. I have searched this forum up and down trying to find someone with the same problems, and while some have been close, no one seems to be experiencing the same issues. Ok, here we go...

For the first 57,000m of my E70's existence it was flawless! Then the following occurred:

12/17/15 - See Attachment
Vehicle goes to dealer because of oil leaking from the Right Front of Vehicle, caused by the Turbo Oil Supply Hose Leaking.
Installed: 11 42 7 795 971 :Oil Pipe (1)
Installed: 07 11 9 905 041 :Gasket Ring (4)

Open Campaign Performed: B 13 06 14 caused by
Recall 13 06 14
Installed: 13 62 7 801 158: Oxygen Sensor (1)

01/02/16 - Driving at 45mph and the HUD shows 'Engine Malfunction - Reducing Power' for the first time ever. I was close to the restaurant so I continued on, and within 3 minutes the error was cleared with no CEL. I continued to the drive the vehicle for the following week with no incidents. Then I found out about a death in the family in NY, and my sisters and I took my E70 diesel from Tampa, FL to NY stopping only for fuel.

Arrived in NY 1/11/16 at 4:00am after 16.5 hours of trouble free flying up I-95. After sleeping and showering I returned to the car at noon to see family. At this point it was 30 degrees outside and within 5 minutes of driving the 'Engine Malfunction Reducing Power' message was displayed again. I tried stopping and restarting the car, which worked temporarily. The car would then do it intermittently during the next 20 minute drive. However, the CEL did come on and stay on for the first time ever!

I couldn't risk a serious problem when I knew we had to leave the next day for another 1,000m trip back home. So I took the vehicle to a NJ BMW dealer and they preformed the following:

01/11/16-01/12/16 – Replaced Faulty Catalytic Converter
See attachments for all the work done and full details.

1/12/16 - Leave NY at 5PM
Make it 200 miles and the car starts doing the same thing. Displays Engine malfunction... but it mainly does it when I slow down to exit speed ~<40mph. If I keep it around 80mph, the car drives perfectly normal. It does take a full minute to hit about 60, then it kind of just goes normally. It did this off and on for the remainder of the 900 miles...

1/13/16 - Returned to FL and made appointment following day with local BMW dealer.

(THIS IS WHERE IT GETS INTERESTING)
1/14/16-1/15/16 - SA calls me Friday afternoon and says they think it's the lower turbo, but won't be sure until they remove it for inspection. SA claims my extended warranty plan (a very good one) won't cover the 5 hour diagnostic procedure. So I need to guarantee payment of about $700 to perform the diagnostics on the lower turbo. If the turbo is the problem, the extended warranty will cover the repair/replacement and I won't have to pay the diagnostic charge. IF IT'S NOT the turbo, I lose $700 in diagnostic fees, plus probably more diagnostic fees for future diagnostics, plus an inevitable $200 deductible to my extended warranty provider for the eventual repair.

(Side note: I called the extended warranty provider and they have no record of the SA calling. The SA claims he called them for a different customer and asked about mine while he was on the phone, and they said they won't cover the diagnostics. I asked the SA to please call in reference to my vehicle specifically, he did, and he said "it has been sent to the drive train division and they will respond in 24-48 hours")

Questions:
Are the turbo oil supply leak and the turbo/catalytic converter failures related?
Should I be skeptical of the SA?
Should I just guarantee the diagnostic charge?
Has anyone had these types of failures before?
Should I sell this the minute the warranty runs out?