A little update...
@Lee got round to the front of the car and got the coil overs out and they look like this:
*Badly corroded.
*One damper not returning to length when spring removed.
*One top mount totally seized and causing one side adjust the height by itself (!).
These are FK Coilovers fitted in 2010 and done circa 25k miles in all weathers including winter. Half my commute used to be on a Kentish A roads so plenty of muck..
I'm not sure if this is good or bad as far as longevity goes.
The top mounts were items from an eBay seller.
So I've looked at replacements and settled on a set of BC's like these:
http://www.corbymotorsport.com/z3-c-1_205_14_86_325_342/bmw-z3-9602-bc-coilover-kit-br-p-952.html
Adjustable height and damping (quite easy apparently with little extenders for the rear damper adjustment. Comes complete with pillow ball camber adjustable front top mounts.
They get excellent reviews from BMW forums in the US.
They sound very well engineered, lots of info here:
http://www.bc-racing.co.uk/br-series-coilovers
Should arrive mid March and looking very forward to transformed ride!!