I had a girlfriend that liked someone buying her gold on a regular basis.
You on the other hand have a John Deere with a problem, hopefully its still in warranty? The only thing that cracks exhaust manifolds is stress. Either it has been fitted incorrectly, putting a pull on the casting or its carrying to much weight. Excessive engine movement may also stress the brittle casting. But your friendly JD dealer will be able to fill in the gaps for you?
Luckily I was able to give her the flick when we left school, your John Deere on the other hand may be harder to cure.