northernchap wrote:Current state of play is that no matter what the height lever is set to:
Front end is as low as it will go and rock hard.
Back end is right up in the air but has suspension movement.
If the car is run, fluid leaks everywhere from one of the pipes that connects the LHM reservoir cap. This apparently should have a Y piece but is a T.
The fluid in the car looks and smells awful.
So I'm about to go and have a look underneath and see what I can see, properly supported of course. Then I might see if I can empty out the reservoir and clean it up a bit with some petrol. I don't have any Hydraflush and the only place I can see any is on eBay so it might have to wait until in the week before I can top it up again and see if anything improves. I could get LHM locally but it'd be about 50 quid from Halfords etc. as a rush job and I'd probably end up having to ditch it anyway once it's been in a little while as it's currently so manky in there.
Front end can be due to several things but often it is due to "sticky linkage" of the height corrector. Spray the linkage through the offside wheel-arch with 3in1 penetrating spray or similar.
Back end could be linkage but usually this would sink eventually if the car is not run. Could possibly be stuck valves in the HC due to congealed fluid, in which case a strip and rebuild may be necessary (but try the Hydraflush first). Your comment that you have suspension movement only indicates that the sphere diaphagms are good and you have pressurised nitrogen there.
If copious amounts of fluid is leaking from that T then something is very wrong as it should only pass a dribble of fluid every now and again as this is a leak-off return. Check the fluid outputs from the Pressure Regulator (Front of engine) and the Security Valve (low bulkhead, visible through back of n/s wheelarch). IIRC if the security valve has failed then that may be the culprit for peculiar operation of the suspension as its function is to retain braking capability in the event of loss of pressure in the overall hydraulic circuits.
As you describe that fluid is leaking from the black pipe (which shouldn't be as it should be a vent) I suspect your pipework has been bodged and possibly the leak-off from the security valve has been re-routed directly here to the vent side of the Y. Normally the leak-off from the security valve is combined with another leak-off via a T piece above the front sub-frame.