Since I don't own the VAG-Com, I can't cycle the ABS system while changing my brake fluid.

I figure that changing the brake fluid more frequently is a reasonable compromise. Even if you do a perfect job, after a month or two, you've got *some* moisture in the brake fluid again anyway.

So what I'm trying to figure out is how often I should change it given that whenever I do, I'm leaving a little of the old fluid behind.

What proportion of the old fluid will be left in the ABS system? 10% ?