I'm sure you know that the clutch actuator is a bit of a weak spot. It doesn't snap the spiral like the 451 and 454
however, it does dry up internally which will slow down the movement.

The only thing that stops the water from getting into the casing is a rubber boot. This one looks fine...



...until you extend it. Then you realise it's split. Considering how low the actuator sits, it can easily take a drink of a puddle.



Pull the rubber boot off. The problem now is that this part isn't available separately from smart.



Luckily there are suitable ball joint seals that fit nicely.



I tried a few options but Martin T came up with the best fitting option.
These are the ones I bought, they are the small size he has for sale.



If you can get the split rings on, try it. I didn't even bother.