I believe you have a caliper that is dragging causing the fluid to boil. Jack up one corner at a time, apply the brakes and release, spin the wheel and you will find the one which it is. It also can be caused by the flex hoses so if they are older than 10 years change them too.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz