Audi A8/S8 Boot/Trunk lock removal changing

[H24K]

I have a 99 facelift S8 D2 and have the dreaded battery drain problem which as of yet has not been diagnosed due to the ridiculous prices these auto electricians charge per hour!! lol and basically my boot lock cant be opened with the key I have which fits ignition and doors etc, maybe it was changed in the past but I basically decided to buy a new barrel and key so i can get into the car when the battery drains so i can start the car and have access to the battery, and am trying to find any info on how to change the lock, if anyone knows if someones posted any info on how to do this in the past would be greatly appreciated if someone could direct me or give me instructions, Thanks