Replacing both airsprings on the Disco2 took 1 hour. Following Urban Panzer's "manual" it is a piece of cake. Springs ordered at Chris McKnight's and toggled along like the "manual" advised. However on two issues I went my own way:
First of all, every manual states that dirt in the airlines can seriously harm the system, so instead of unscrewing the lines completely from the compressor valveblock I unscrewed them just far enough to let the air escape, making capping off the open ends unnecessary and avoiding the risk of ruining the threads (esp. because the sidestep is a wee in the way, making the compressor unit somewhat difficult to approach)or mixing them up .
The second diversion was at the end of the airhose where it enters the airspring. In my case the hose was topped off with a open "o" ring that would squeeze into the brass union a therefore making itself airtight. I carefully opened the ring and was able to slide it off - hereby saving (scarse) line length, because I didn't have to cut them off.
Pushed the line into the fitting and returned to Panzer's manual. For which I am very grateful.

also did mine recently using up`s manual. but instead of releasing the air from the compressor valveblock. i heated a thin blade screwdriver till it was cherry red and inserted it into the airbag. probably not recommended, but worked for me.

I did my airsprings last staurday > Also slid off the brass olive instead of cutting the line . Put on new sensores a few months ago . Problem still persists . I know that at rest it lets itself down a bit but should it go down so far taht the arches are over the top of the tyres . Looks like "loaading" height to me . It used to be before changing the air bags that the offside sat lower at rest than the drivers side , now it is the other way round ! It blows itself up to ride height within a minute and will carry on the extra few MM if i ve pressed the "off road height " button . Is it time for a trip to the dealers to get suspension calibrated ??

To answer my own question, nice quite windless day outside and hey ho heard slow leak from the valve block , the offside O ring had split , replaced this afternoon and so far all staying nice and level

Urban panzer s guide to air suspension is a must !!!

Like Urban stated, check for leaks - at the valveblock and only close the lid after you're satisfied with it. Still.......job done!