central locking

[paulcl]

v reg 1999 s40 driver door. when i lock with the key (as i dnt have a fob) the knob thingy goes down, but the door isnt actually locked, i can still open it simply by the door handle, and when i unlock the doors, the drivers knob thingy stays in the down position.
it does move a little and i think its had prob b4 as the knob has marks/scrathes on it as if some1 has screwdriver'd it up,

ive read previous posts and it appears to be sticking, so i removed the door panel and wd40'd it, it worked fine, until next morning, and the knob thingy didnt come up again. so i removed panal again and oiled it rather than wd40, i noticed that the actual metal rod appears slighty bent in places, so i tried to straighted best i cud, whilst it was still connected.
but as soon as door panel back on, it stays down, and i cant see any obstuction that would prevent it.

can a new rob be purchased? and is it easy to do, or any other suggestions as at the mo my car "looks" locked but actually isnt and as i dnt have a fob i cannot alarm it, so it can be robbed :-( help pls