Nice one mate! You're obviously a handy chap. Water ingress around registration plates is something that really annoys me! Why build a beautiful car, spray it and then mount the reg plates by drilling holes through the door! My wife's Rover 200 had a problem with the rear door. Every now and again it would just pop open and then be very hard to shut again. With the help of my good old Dad we took the interior trim off. The reg plate had been screwed on and water was running down the inside of the door. A quick squirt of WD40 and some Waxoyl around the screw holes and we've had no further problems. Why not just stick 'em on with a bit of tape I'll never know!