Thanks, I'll give that a try and hopefully I can sort the seepage out.

I have been using Automec Silicone fluid for several years in the braking system of my ZB without any problem. I renewed all the lines, hardware and rubber at the time and I did find I had to tighten the banjo bolts at the rear very tight to get them to seal. It might help to anneal the copper washers to ensure they are soft. Just heat them to cherry red heat over a gas ring and quench them in coldwater. I have done this successfully with use-hardened washers when new ones were not immediately available.

Having successfully used Automec Silicone Brake Fluid in other cars, including my Wolseley 6/90 which has had it without problems since 1989, changed once. I decided to put it in the Magnette after a complete brake rebuild. I cannot stop the banjo unions on the rear brakes from seeping fluid. I get a good pedal and the brakes work well, however the rear tyres show evidence of silicone on them and the master cylinder level goes down slowly. The car has been off the road for 14 months for a body rebuild, the brakes remain fine, but when the car came home the m/c was half empty.
I have previously replaced the copper washers on the banjos and checked the surfaces, all look OK. I replaced the washers again and used a Loctite sealant recommended by them, no improvement. I am now considering trying Dowty washers.
Does anyone have experience of Silicone Fluid in a Magnette and if so any thoughts on how to get a good seal - one cannot just keep tightening the bolt! I am reluctant to give up and put conventional fluid back.