I also have had to to replace my clutch actuator recently. Like the OP, my smart is a 2008, but with only 38,000 km. The key to the part failure was mostly due to years of service I believe. Because, after removing the part and opening it up, I immediately noticed the gasket was out of position in one area (like the OP). As a result, there was quite a bit of corrosion on everything, including the broken spring and broken worm drive off the electric motor. I'm sure the actuator would have been fine if the gasket had been seated properly and done its job of keeping moisture out. Special thanks to Glenn for helping source a new actuator. The gasket on it is seated properly. In addition, I put a bead of silicon around the outside of the seam.
I don't know how prevalent this problem is? It might be worth it for others to have a look inside to check the gasket and investigate possible corrosion. The actuator does need to come off the car (3 bolts and a plug), in order to remove the cover. I jacked up and blocked the rear driver side to gain clearance to access it. Hopefully (and likely), this problem is very rare. The car has been very reliable for me over the years other than this issue.
