I double checked and per MINI it is 30Nm for the oil feed banjo and 35Nm for the coolant banjos,... Maybe what you are feeling is the copper crush rings giving in (deforming)? Causing the impression that you are stripping them? Just a thought,...

 

The threads are not stripping. The bolts are shearing under the torque. I can see a crack in both bolts that have failed at where the thread starts up near the radial oil supply holes. I confirmed with Detroit tuning the 22 ft-lbs (30 Nm) for the oil supply line. They use the 22 ft-lbs, no problems. I am going to tighten to what I am comfortable with, probably the 17 ft-lbs . This has happened using two different torque wrenches, so I cannot believe they are both out of calibration.

 

2008 Cooper S turbo oil supply line install lessons learnt:
1) Put the vehicle into radiator service mode. The 2-1/2" extra clearance makes all the difference. I was even able to reinstall the upper screws for the lower heat shield. Assume you will break all the clips that retain the wheel arch extensions. There are 14 of them. I ordered 21 of these as they do get used elsewhere. I needed an assistant when pulling the front section along the lower support tubes both out and back in.
2) I had problems with the banjo bolts. They kept shearing at the specified torque when installing the Detroit Tuning hose. DT confirmed the 21 ft-lbs. HoweverI torqued to 18 ft-lbs as I was down to my last spare bolt. Suggest that 2 new spares are ordered along with the copper washers.Try to use original bolts, but if they fail at the suggested torque, al least you can plod on.
3) Use a proper O2 wrench kit.I got mine from Autozone on loan.
4) I replaced the down pipe to turbo gasket and the vee clamp between down pipe and muffler system.

I had no leaking from the oil filter housing or the turbo oil return line, so left them undisturbed.

Final comment. The original design is a waste of space. Putting a rubber o-ring next to a turbo!!! The first time I saw that I was disappointed that BMW did not use a compression joint....like the DT part. I am also disappointed that the replacement part from Mini is the same design.

Now to get back to enjoy driving the car!