Hmmm ... tough call. I think what you did was about the maximum you should/could do - good for you! In particular, I would not recommend entering any car to go beyond that.
A similar (not cars though) thing happened to me once. My neighbor was away on a trip and one of his water pipes (fortunately outside the house) broke. It was spilling large amounts of water at the side of the house, along the fence, and running out onto the front sidewalk ... pretty clearly a major break. I felt comfortable going into the walkway next to his house where the water was coming out of, and found the break - could not fix it though.
But if the break had been
inside the house, I would not have felt right about going in though ... he might have been okay with it, but that would have needed me to somehow break into the front door, etc.
Anyway, I turned off the main water valve in the front (sidewalk cover access) and left a note on his front door as to what I had done. He was very grateful when he got back a few days later, since his water bill would have been enormous and the damage to the garden and walkway next to the house would have been quite bad. I happened to see him a bit after he got back while he was still wondering why he did not have water inside his home (had not seen my note on the door yet, since he went in from the garage). He called a plumber before unpacking the car ...
Z