I’ve got water leaking into the boot of my 2009 focus. It’s on the right hand side and looks like it’s dripping from above the boot light. Has anyone had this problem and found a solution?

Try applying a good coating of grease to the foam on the rear of the light clusters. Don't use silicone as they will be a nightmare to remove when you want to change a bulb.

Check any cable entry grommets are seated correctly.

Also worth checking around the hinges and damper mounting points.

 Leaking bodywork seam sealer is another possibility and happened to me on my wife's car.

The best way to find it is to sit a hose on the roof and leave it running for a while to see if you can find the entry point. As mentioned by a fellow member a smoke machine inside the car is a good way to track a hole down.

The mk3 (can happen on yours too) is also prone to leaking cavity vents but these are lower and located behind the rear bumper. It causes the cavity to fill with water and then spill over into the car when it reaches a certain level or cornering which then collects in the spare wheel well.