A leak-down test is performed
A leak-down test is performed by pumping compressed gas (like nitrogen) through a regulator and through an expansion valve down a hose into the cylinder through the spark plug boss. You can buy these things as a kit, just be sure to find on with a fitting for the Ferrari spark Plug thread.
Bring engine up to temperature, then disassemble the spark plug ccovers, remove spark plug wires, remove spark plugs. Position the cylinder under test at TDC on the power cycle (both valves closed).
There is a guage reading line pressure and a guage reading cylinder pressure. If you can get the line pressure guage to read 100 PSI then the leak down number is read directly off the second guage.
After taking the leak down reading, you can then listen to where the leak might be occuring to isolate intake valve/seat, exhaust valve/seat, rings/upper cylinder :: using a mechanics stethescope.
Cost:: Figure 2 hours labor.