That water comes from the brilliantly located drain hole in the driver side wiper spindle assembly that cleverly sends rainwater to cause a failure from rust over time. Incidentally, that same drain hole regularly gets blocked from tree debris causing water to overflow from the channel onto a module under the bonnet that can then fail. Double whammy.I have a 66 plate and had a quick look to find no covers and water in the drivers side top mount. It only takes a few minutes to pop up the plastic trim and have a look.
The cure is to poke that drain hole clear from time to time and fit a cover over the strut top area to shed water away and down the interior wing to the ground. I used an upturned empty yoghurt pot that was a tight fit over the entire area and solved the strut problem cheaply and effectively. And as the drain hole is a bit difficult to locate I threaded a length of bell wire through and twisted it to stay there for next time the hole needed clearing out.