At 1 AM, the lake in Santa Barbara is 2.5 hours from Disneyland. There would be no need to stop for fuel in a BMW. You could very easily make it from Disneyland to Santa Barbara and back on one tank of gas.
Let's pretend for a minute that he did have to stop for gas. Do you honestly think that we would hear about that surveillance video? There is no way the police are going to play the cards that they have and let the defense to see their hand!! They don't tell the public about the evidence for good reason!
Also, that witness at the lake was never discredited. Police just refused to say whether her statement was being taken seriously.
Who led him to the lake? Who cares? Probably Google maps on his phone. The point is, he was seen there on video, and his son was found dead there. That pretty much tells us all we need to know.