The lock cylinder can be tricky to fit if you don't understand that the hex bolt that holds it in can never pull the lock cylinder in tight, as both the cylinder assembly AND the hole DHC the bolt threads into are threaded.
The gap that exists once the bolt threads start into the DHC is the gap that will remain, not matter how tight the bolt is.
The trick is the hold the lock cylinder tight against the car as you wind in the bolt. And don't over-tighten it. It can be hard to get right...
