Audi TT mk2 - Central Locking issue

Hi

Having some problems with my central locking. The key fob is working fine, drivers door opens fine, passenger door doesn't unlock the first time and have to open from internal door handle, however if from the keyfob I unlock, lock then unlock a second time it works, and this seems to happen every time. There is an audible difference from the first light cluck to the 2nd time solid clunk as mechanism works as it should. Short of spraying some wd40 into the mechanism (didn't work) not sure what else I would need to do

Has anyone experienced this before and knows the solution and if it's a DIYable fix.

Thanks in advance.

Pete