Hi,

If you're 100% confident the oil separation and scavenge system is working correctly, it could be an operational issue:

Make sure to always stop the compressor with outlet valves closed. Let the compressor run unloaded for some time before stopping.

What do you use the air for? This problem often occurs with blasting or other intermittent air use (on/off/on/off) - the separator can't handle the fast flow of pulsating air and oil will carry over into the compressed air.

Please let me know if this helped or any other info that might be useful.

Thanks :)

Cas