I have 130 thousand miles i think you'll be okay. I wouldnt put it in the oil though. I did it and it ate my oil seals I dont know why, and it made the oil leak out main and etc. I was told by a mechanic after you put that junk in your oil and change it some of it is still in there and will be for a little while, not sure if thats true though, all i know is that seafoam eats through stuff.
I would suggest putting it through the hose, and fuel tank.