of the '80's and '90's only lasted 100K miles anyway, but old and worn out brake fluid can start to entrain air and give your brake pedal a spongey feel. Which means you have less stopping power than you should.

$100 isn't necessarily a ripoff to do it (all four wheels must come off and it helps to have two guys to do it), but it is a decent profit margin for the shop.

I've done it before when one of my vehicles reached 100K and noticed an immediate difference. Should have done it sooner.