you will have to remove the lock barrel assy from the door,big horseshoe clip and linkage to remove,you will need a lock kit to overhaul the barrell and your key no. to input the correct sequence of plungers into the barrell,the key no. will be something like T142341 and the plungers are numbered to suit your key and inserted into the barrell in the correct sequence,if you haven`t done one before would recommend to get the barrel to someone who has done this before,only takes 10 mins to build up,by the way have you had a look at your key,bad for wearing and a new key may sort your problem
cdc, January 2011