If you go the rebuild route I did my ps13 coffin recently using a Brembo kit. I got the pressed in ring out by using a punch down one of the threaded holes for the cover to cave it in a bit so it could then be pryed out. Installing the new ring I used a socket in a press. The ducatipaso.org link above has good info and pics.
As the repair kit has a new piston assy with seals already fitted, and a new end seal and lock ring, you can remove the original one using a thin punch down the cylinder outlet where the banjo bolt fits as the original piston is going to be scrap. Put a bit of rag at the lever end to prevent damage to the m/c body and this also keeps all the parts on the piston assy when it’s removed so you can record the correct orientation of the parts to help with reassembly. Only takes a sharp tap to remove the piston and lock ring assy. Before disassembly you can also do a drop check with a vernier calliper and measure the distance from the end of the master cyl housing to lever end of the piston as well as the locking ring, check the replacement piston is identical, and remeasure after installation to confirm the replacement locking ring is fully home.
