FWIW, I have the Legacy IO-550 and no separator installed.  Factory new engine with almost 700 hours.   I go through about 1.5QT of oil between 25-30h oil changes (W100).  I have a small amount on the belly to clean off and the breather exit is located on the bottom. Compressions are high 70s on all the cylinders.

The breathers on my previous TSIO-520s (Cessna) experienced freezing at FL altitudes and Cessna had drilled a hole at the top of the tube and facing upwards as a safety measure if blockage occurred.  Is there any chance that temperature is playing a role in these incidents?

Paul
Calgary