Then I'd deffinately say it's fine. You'll know it's slipping when it doesn't shift when it should, shifts erratically (indecisive about what gear it wants to be in), and shifts hard. Until then I wouldn't frett. Usually it'll be a gradual change you will notice if it's going to go out - usually. But as I said, I've got over 250k on my tranny and it's smooth as silk.