I have an aluminum back door with a very old lock that started jamming. To be honest I didn't expect it to be that difficult to change it, I tried to do it myself. I was able to take it off the door but couldn't find a replacement lock anywhere so decided to just call locksmith. Very helpful chap - he phoned all his suppliers and at the end ordered the lock specifically for me.I realized watching him work I would never be able to actually change that particular lock. He did it really well, it fits perfectly and the lock itself is solid and high security as well.
