The following instructions on the repair of the boot lid locking mechanism is the work of Michaela/MikkiJayne/D2 Doctor and is a single post extract from one of her threads. I've posted it as a separate thread to make it easier to find.
------------------------------------------------------------------
Also fixed the boot lock since it was seized completely solid
Removed via the door for for the light cluster
Disassembled the main body
The lock barrel was completely seized in the housing. Lots of WD40 and wiggling and it finally came free.
Crusty!
Started removing the tumblers
All disassembled. It took about half an hour cleaning schmutz out of the barrel with an assortment of pokey tools, degreaser and compressed air before the little door would close again!
Cleaned all the tumblers up
Reassembled prior to re-greasing
Going back together
You can see the cam which operates the central locking here via these two microswitches
All back together and ready to put back in
__________________
2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts
My DIY jobs -
Replaced alarm horn,
Replaced Coolant Temp sensor,
Updated RNS-D firmware,
Installed Reversing Camera and Digital TV,
Dashcam Installation,
Retrofitted Rear Blinds,
Auto-Dimming Rear View Mirror,
Chrome Boot Struts
Sold! 
2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights
My DIY jobs -
Fan Jet Windscreen Washers,
Retrofitted Electric Side Blinds