Gas cap warning light problem

[wwu123]

Hi, recent purchaser of a pre-owned '07 X5 3.0i about six weeks ago, and new to these forums. I've been happy with the car, but I've had one problem so far, the gas cap warning keeps coming on and triggering the check engine light.

First time was after my first fillup, so possibly user error that I didn't tighten it enough. I had to bring it to the dealer service dept to get it cleared.

But later on, about 300 miles into another tank, the gas cap warning diagram in red would flash for a second or two and disappear, then it flashed again and triggered the check engine light again. The light has stayed on for the past 200 miles. I don't think it was user error this time as it was fine for 300 miles.

1. Will the check engine light clear itself eventually? Or do I always have to take it to the dealer?
2. Is there potentially a faulty cap, filler tube, that is the cause and would need to be replaced? I am at 49,000 miles, so want to have them check for any repair parts before the original warranty expires.
3. Could it be likely caused by temporary factors - water in gas, low-grade gas, cold temps, or coming down from high altitude (was in Lake Tahoe the previous week)?