Yes, it goes all the way thru. I stuck a screwdriver in there (carefully) a couple of inches with no resistance. All the bolts I put in there were the original bolts with the washers that don't come off and are quite short. So it wasn't me! lol.

And I reinstalled a new bolt with sealer this time (and took out the other one and put sealer on it, too.)

Drove it to one end of town and back and no leaks.