Stop searching the old tunnels. Go straight to the southeast boss chamber on Snake Lair B2. Mark the spot 440, 640 on your map, set a 55-minute timer after each kill, and you will have a stable boss farm route.
If the location is fixed on your server, you will see: metin2 chuong location fixed
Respawn Timers: ~22 minutes (Upper area) and ~20 minutes (Lower area). Stop searching the old tunnels