Boot lock jammed

The boot lock on my 6n (central locking removed) has stopped working properly.

I can now only unlock the door by turning the key slightly to the right then back again and pulling it out. 

Previously I would turn halfway to the left and that was it’s normal unlocked state. Can get by like this but obviously not ideal and it doesn’t feel particularly good. 

Anyone else had this problem and what did you do to fix? 

Thanks