If you get water dripping on the fuse box:
Remove the RH speaker cover screw. When it rains, whip off the cover and check that the RH corner of the windscreen seal is not leaking. (You could always pour a bucket of water over the top of the screen, too!)
If you go to the scrappy and look at the mk2s where someone has removed the windscreen, they all have rust in the bottom corners of the windscreen.
Fix it by spraying waxoyl (or even better, Dinatrol) under the windscreen rubber from top to bottom.