Technically, using the evidence seen on GT5 that an engine always looses power if you continue to drive it and don't change the oil or rebuild it, I guess the answer would be yes.
Whether that's been done before and it's actually true, then I don't know.
i have tried that on my FGT, and after complete 3 or 4 tsukuba 9h endurance races, the hp stop dropping. It was 750cv or a bit more, but from there, it never dropped down...