BMW Repair: 525i Touring M reg 1995 exhaust smoke, mont blanc tunnel, wet patches

Question
We have recently purchased this car second hand. During a drive from UK to Italy we noticed white smoke from exhaust, it didn't last long,it happened at altitude approaching Mont Blanc tunnel. The engine oil level appeared okay but unable to check transmission oil level as unsure of location(new to BMW's) The cars response to demand got better as we reached sea level. The only other thing I noticed was the tail gate had a spray of oil on it and the underside of the car had wet patches from about below drivers seat location. I also felt that the Aircon was not performing well, when on it never effectively cooled the cabin (OAT about 28 degrees Celsius)

Answer
White smoke is normally caused by coolant in the system,has the level dropped at all?Having oil spray on the back and under the vehicle should be checked out as an oil leak is an unmeasured air leak that the computer cannot compensate.Have the a/c recharged the freon might be low.