Wot he said. Multitude of leak points and how to's that fix them. There are some novel suggestions as to how to find these damn leaks, depends, but I'd suggest you work through the 4-5 most common one's first. Silicon will work but IMHO the best sealer jallop is Sikaflex 521UV together with Sika Aktivator 205, bit more expensive than silicon but made for the job.