From the beginning Smart have always had a problem with cracking turbo exhaust manifolds on their three cylinder cars.
This seemed to eventually affect every car at some stage or another, making the vehicle pulse under acceleration.
First signs from the wastegate mount (click to zoom)
Second crack from main 'bridge' of the manifold (click to zoom)
Third crack on the exhaust side from the wastegate exit (click to zoom)
Fourth crack on the turbine side from the wastegate exit (click to zoom)
The solution was to recast the design from this:
To include a reinforced bridge and thicker walls:
This modified design was bought in on 2002 cars (Mk6 onwards) to try and combat this on going problem. This new design seems to increase the life of the manifold by a fair amount, however it hasn't totally cured it.