I`ve just bought a 1997 850 awd (paid £3500 for it-good or bad price?)its done 72000 miles,i want to change the oil but am at a total loss as what to use mineral, semi synthetic or fully synthetic. What do u people use on your turbo engines-have heard some bad reports about switching to fully synthetic. I have also got a leak, looks like turbo return line, is this as straightforward as it sounds to replace or am i likely to have problems? any help on these matters would be appreciated.