| I've had me 998 boil up it's rear fluid a time or two, I do tend to use the rear brake quite a bit.
A fluid change could well cure it, if the fluid is old it boils more easily as it's hydroscopic and the increased water content lowers its boiling point.
Brake fluids have a dry and wet boiling point. The wet is usually a lot lower, in some cases an couple of hundred of degrees lower.
Ray. | 
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