How to strip rear brake compensator?

i want to strip my rear brake compensator/regulator as part of my ongoing resto. It looks like the nut on the actuating lever should just unbolt whilst holding the little piston rod using the slotted end, but mine won't budge.

anybody stripped one before and can offer any advice?

I did attempt this myself but gave up pretty quick, instead I binned it off and converted to a mk2 one as the mk1 units were far to expensive when I needed one:
http://vwgolfmk1.org.uk/forum/index.php?page=topicview&id=your-mk1-golfs_2%2Fproject-83-mk1-cabby