What to do when multi-lock key doesn't go into the lock easily?

Tweet

We have a multi-lock at home, and for some reason lately it's been difficult to fully insert the key into the lock. Last time my hubby tried to do that his key broke in half, part of it left inside the lock. I never knew it was even possible for a key to break in half. We were thankfully able to remove the stuck key from the lock, but now my hubby is left without a key, which is not good. I thought of making a copy for him, but I don't have the multi-lock card. A locksmith won't make a copy of a multi-lock key without the card. My dad tried to make one for himself, months ago, and no one would do it for him without the card. Even if I find a locksmith who will make an exception and make a copy for me, there is no point in doing so as my key doesn't always go in easily, or fully, and I have to force it in. Sometimes, it's even hard to turn the key to lock the door. Seems to me the only way to fix it is to replace the lock. Am I wrong? And if that's the case, should I just replace the part of the lock where the key goes in, or install a whole new lock? And if I just replace that part, how do I know it will fit into the lock?