I'm hopeful that I may have cured my water leaks.
I sealed under the tailgate rubber seal and around the tailgate hinge brackets that attach to body. Water still came into boot at the same place as before.
Did water testing from the bumper upwards and found that water only found in boot when I ran water on roof around the rear roof bar bracket,
I removed the bracket, cleaned the whole area up, put some sealant under bracket, gasket, bolts and on the bodywork seam along side the bracket.
It was impossible to be certain that this seam was intact , it looked a bit dubious in a couple of places, thats why I sealed it.
Re assembled roof bar and done 2 water tests since and NO WATER in the boot.......................................at the moment!
I am hopeful that this might be my answer to my problem. Time and rain will tell.
This info may be of some help to anyone still struggling with this problem.