Vacuum pressure is very important Any leakage would cause performance and emmissions issues as turbo is vacuum controlled and the so is the EGR valve,by solenoids.(electric switches).
Even your engine mounts are vacuum controlled!When the mechanic does the vacuum test ,he will see vaccum hoses going to left and right engine mounts(these are only on auto transmissions X5s!)

Ok..dark brown colour on oil is good,just ask them what viscosity oil grade they filled up?Both 5W30 or 0W40 are fine.

If smoke smell is also diesel,just confirm the glow plugs again.You may also have a leaking injector but this should have been diagnosed!A leaking injector leaks mostly when engine is stopped and fuel is deposited in chamber,so when you turn engine on,this will come out of exhaust as unburnt fuel.!Glow plugs as you know,are there to heat up fuel in sub-zero temperatures ,so this time of year they are only on standby,really.

Get the mechanic to remove the turbo outlet pipe ,(the black rubber 90 degree pipe tha is directly under the air filter box) and check for excessive oil in the turbo and the play in the compressor!