If the Door is a Henderson Ric, you can get the lock from their County Durham works, I have done this, to fit the lock will take about 10mins, If the door closes with the lock do not waste your money replacing the whole thing, the Up-over doors are very simple to use, if the runners within are ok & the wood that they are fix to is in order the only other replace parts are the roller ( 2) they are not that expensive from the same place, Henderson, let me know & I'll see if I can help you.