I haven't tried the LiquiMoly product, but I've had very good experiences with another diesel system cleaner (see:
/viewtopic.php?t=18828&highlight=).
I had very poor compression readings (35-39-39-21) and was advised to use a cleaning product to remove potential carbon buildup on the valves. Because of the unpleasant prospect of having to disassemble the cylinder head and grind in the valves, I decided to try it, and – voila: the compression readings are now 34-34-32-34! Since then, the car has been running perfectly again, and I'm using about half a liter less fuel per 100km with the same driving style. By the way, along with the recommendation, I also received the note that the excessive compression caused by oil carbon buildup on the pistons can easily lead to engine damage, and that this is a much more critical issue than the leaky exhaust valve.