PES
After about the first year/5000 miles the petcock on my 03 TA started to get tight. It didn't matter if it was overnight or later the same day, it just became hard to turn. I replaced it with a Pingel, and that was the end of that problem. As to how gas can get in your crankcase, with the petcock left on, if either of your floats or float needles, or float needle seats have any deposits on them that prevent a decent seal, gas can get past them into the airbox or into the cylinder. Depending on the temperature, this could be vapors, or in an extreme case, raw liquid fuel. If it's in the cylinder, it will pass the piston rings and get into the crankcase where it will displace the oil on the bearings and cause damage. If it's in the airbox, the first firing of a spark plug will ignite it and you will be picking up pieces of plastic from beneath and behind the bike.
I have developed a habit of observing the following when I stop riding.....
Shut off the petcock.
Shut off the key..
Put the kickstand down...
My butt doesn't rise from the seat till all 3 are accomplished.....
