This is Porsche 911 (996) Carrera engine. It seems to me that liners can be removed from the block. I think this is a wet liner engine. Am I right?
In an effort to reduce costs during production, Porsche utilized a type of insert-mold casting process to directly incorporate Lokasil cylinder liners into the case. While this is a neat way to reduce the total number of parts used in the engine, this design basically casts a wearable part into the engine case. There is no factory replacement for the liners, when they wear, the factory expects you to buy a new engine case. In addition, the design of the cylinder liners allows them to "float" within an area filled with coolant.
Excess vibration and twisting from the normal operation of the engine appears to be causing some cracking in these liners, resulting in a small chunk of the liner breaking off. When this failure happens, you will see oil and coolant begin to mix together or a slight unexplained coolant loss.
If your engine experiences this failure, it can be rebuilt using LN Engineering's Nickasil liners installed. They take your old case, machine out the cracked or damaged Lokasil liners, and install an aluminum Nickies insert, which is stronger and more reliable than the factory cast-in liner.