Master cylinder was replaced 6 months ago, no issues since. However, today after two days of below freezing weather and no driving time in that time period, I came out to find that my clutch pedal just sank to the floor. I checked my reservoir and I couldn't see any oil whatsoever. I filled it back up and drove it around for about 20 miles and the clutch is fine again. No signs of leakage above the fuse panel. Any ideas on what the issue could be? Could it somehow be the cold weather?