Don't think it will be a 300Tdi, isn't P reg 1997/98 in the UK? In which case it will be a P38a second generation model, and if it is a diesel that makes it the BMW straight six unit which is why it is a bit quieter than a 300Tdi
FWIW I looked at buying a second generation RR before I got my Discovery in 2002 and I decided that the reliability record of the electronics meant that by the time they were a price that I could afford, they would be of the age when one ought to be thinking about selling it rather than buying it... I do still like them though