There is a minuscule amount of difference between DOT3 and DOT4 fluids and it would have no effect on wear. The difference is between boiling points and freeze points.

Whaddya using the brakes for anyway? Getting timid in your advancing years?

The accelerated wear is probably being cause by moisture accumulation. How often are you changing/flushing the fluid?

You can't treat the FF as a car. I'd recommend no more than 10 hours brake use per flush.

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