Sequentronic Gearbox

I have been driving a C220 Coupe Sequentronic for about 6 months (20,000 miles), and am not at all impressed with the gearbox - a shame as the rest of the car is great!
Sequentronic is mercedes semi-automatic, and it feels like a first prototype. It is sequential, but also has an automatic mode. The car has now been into the dealer for 2 services, during which they have loaned me an A-Class. The gearboxes in the A Class (semi auto and manual) are far better than the Sequentronic in my car!
In manual mode the changes are OK if you accelerate gently, and lift off the accelerator before changing - although a friend said 'a bit like a learner'.
However the auto mode is a joke - in traffic, when gradually acelerating the change to second is terrible, and if you lift off, then accelerate it often seems to get confused and takes a few seconds to decide which gear to be in. The car has a cruise control function, but in auto mode if this is set to a limit, sixth gear is not used. Anyone else with a Sequentronic know if this is normal or a fault on my car?
This is the first auto I have driven, but it seems like the auto mode is set for a petrol rather than a diesel as it doesn't change until pretty close to the red line, even with only half throttle - a waste of time in a diesel.
The dealer said that the gearbox is 'not one of mercedes best' and that they have has to replace a few, although when I complained they made it clear that if a fault is not registered by the computer there is nothing they can do.
What experiences do other Sequentronic owners have, and what has the dealer done about it?

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