I just need a bit of advice really because if there is a bad situation looming I think I'll get my local garage to fix this - it looks like a pain to get at it all. A few days ago I replaced both wiper arms on my 1996 300 TDi CSW - it was difficult to get a full engagement of the male splined shafts in to the female splined recesses in the arms so I lightly (and I mean lightly) tapped them home with a nylon hammer with a soft cloth inbetween.

Since then I have a "once per cycle" click as they operate - what am I likely to have done in doing what I did? I have Googled this and there is plenty of references to it but it's difficult to pick out the multitude of possibilities without being familiar with the mechanism.

You may have damaged the coiled wire drive. It's not a major job to change it, but a bit fiddly.

What you have done by tapping is bend the tab on the back of the wheelbox's out of place allowing the spindel to move in and out as wipers change direction.
To access remove top of dash and free instrument panel,4 small screws for air vents and 3 large screws by screen and one hidden under the Land rover badge on nearside,there are also some small screws near the drivers door.
Once off you will see the back plate of the wheel box, two small nuts to remove and then bend the tab in the center forward [not to much] to take up slack in the drive.
Test before replacing dash.

Thanks guys for the info. I guessed that whatever advice I was given the items already provided by tottot would need removing for investigation - so today I bought two new wheel boxes and a drive cable. They have been on the vehicle for coming up to 20 years so it would be foolish not to replace them - a bit like separating the engine from the gearbox and not considering a new clutch.

Advice appreciated

Mine clicked because the wiper adaptor was ever-so-very-slightly loose on the spindle.
Not loose enough for it to pull off, but loose enough for it to click on every cycle