diskutil verifyVolume / : POSIX reports: Exec format error
You can use the Disk Utility application from the recovery partition to do all of this (unlock and mount the disk, run repair, etc.). If you have any other disk repair utilities maybe give them a shot? Either way, if you don't have a backup already I'd make a copy ASAP.

Another idea is to boot into single user mode (Command-S on boot) and run fsck but not sure it'll be any different.