I had the same problem several years ago when replacing the battery, EKA code wouldn't work, ended up removing the door lock (a bit fiddly) couldn't strip it as such, so I drenched it with WD40 whilst vigarously 'working' the lock, loads of old, mucky oil/gunge came out & a can later, it was re-fitted, luckily for me, it then worked & accepted the code!
A word of warning, stupidly, I left the keys in the ign & shut the door, then as soon as I hooked up the new battery, the car went into 'lock-down' & locked me out! somehow I managed to cobble up a coat-hanger wire hook placed into the door-seal & get back in!!
Second warning, I'm so scared of this happening again, that If ever I need to remove the battery for whatever reason, I hook up a little old 12v alarm battery via a couple of crocodile-clips to the pos & neg leads, this keeps the cars electrics powered up thereby preventing sync/memory loss.
