brake judder

Although I have no idea what juddering is, this could be many things... Rotors which are out of round are a first guess.

Do you feel any side to side wiggling when this happens?

Try stopping with the emergency brake only and see if that does the same thing. If so then it's a problem with the rear wheels and it's not related to hydraulics.

Good Luck, Marty

Actually I don't mean out of round... Sorry! I mean warped or not flat.

Assuming that the OP's term "juddering" means "pulsing at slow speeds" or "vibrating at high speeds", then I would think like you in that the rotors are not true (i.e. warped). This can usually be resolved by having them turned on a lathe, unless they are below spec. If they are below spec (i.e. worn thinner than manufacturer's recommendations), that could be what caused them to be warped. However, rotors can also become warped when overheated, as could happen with a stuck caliper or other system defect. In either case, a good inspection of the brake system is in order.

If so, then it could be a wheel or tire problem.

I'm not certain about this particular, but the emergency brake may use a separate drum and shoe system for the emergency brake, so using it will not even engage the rear discs at all. This would, however, help rule out any tire or wheel problems.

Possibly warped discs.

Could be a couple of things. You'll need to have somebody that knows these cars very well look at it. Rotors shoulebe measured for out of round and replaced if not (they're stupid cheap) and if they're ok it could be a suspension (monor) problem.