Which brake cylinders?

Hi there

I need to new rear brake cylinders for my mk1 gti. It's a late 1984 model (campaign). I called GSF today to buy some and they said there is 2 listed. 1 is a steel type and 1 an alley type. Does anyone know which type i will need.

Thanks

the 2 types are bias valve and non-bias valve equipped cars:
http://www.vwspares.co.uk/g1brakes.php

you can find the valve in front of the rear beam, with a spring between it and a bracket on the beam. your car almost certainly will have a bias valve if its a tintop gti