"High mileage" oil use

My wife grabbed the wrong oil–got high mileage syn for the lawn mower instead of normal syn. So, I read somewhere that if you put high mleage oil in a car, you should never go back or you may suddenly have leaks due to shrunken seals. Is this true? Should I exchange this oil rather than use it in my mower?

Personally I would not worry about it.

If you are worried about it just exchange it . Of course I am like Mr. Barky and would just use it and put the proper stuff in next time.

I don’t think I’ve hardly paid attention to whether it’s the green label or the gray or whatever. They just have too many choices. Not many seals there to worry about anyway.