jump through the back seats(litterly
get a small flat bladed screwdriver and shove it in the small slot in the top of boot lock. boot should be open now
undo all the little round clips, (turn 90' and pull the center partly out, clips should then be pulled out easily)
(they are £1.30 each! so try not to break them)
check the wheel well for water as it tends to pool in there if theres a leak off the boot drain hole.
pull the interior panel off, mind the clips at the top, the 2 handles should unclip (with force).
once inside the boot panel, unclip the two switches, push them down and out, unclip the cables from outside(easier).
clean them out any water in there shoudl come out if shaken, chuck some WD40 in the switches, refit
dont forget to wd40 the glass hatch lock and all electrical connectors in the boot.
there is supposed to be a (service part fix) water shield that goes over the switches, you could improvise with a plastic bag
next undo the 3 bolts holding the wiper motor and check that the drain plug pipework is connected ok to the panel where it drains into(middle), is the pipe clear and draining ok ?
a little mastic is needed if its come off, refit
chuck loads of wd40 into the boot lock, (its gonna pour out so dont stand under it when u do
check number plate lights, then refit the inner panel.
your done, it shouldnt need more work now, and you just saved on: parts.£35/£25, +£65 fitting.
the switches should only be changed if the rubber on the exterior of the switches has perrished or gone slimey(you'll know what i mean if it has.)