I bet that's the black one, which will recover all lost horsepower with every oil change. A new GT - One, or a new anything (apart from the FGT and the 1bhp efforts from the stone age) loses something like 5% or 10% of its original power as a maximum after oil change, and takes 8000 miles to do so. Second hand cars with high mileage have already past the 8000 mile mark and have therefore already lost all the power that they are going to lose. They will therefore recover to the same point after every oil change.
A certain ammount ends up gone for good but an oil change brings some back, from then on though your stuck on a cycle of losing that ammount again and then an oil change bringing it back, but the original maximum power is never attainable again after a certain ammount of usage.
I have a 1988 Holden Commodore, that has done over 1,000,000km (621,000m) (no typo) and I can guarantee that it has a darn sight less HP that when it was brand new
