MacOS – Finder Reports Disk is Full, Other Tools Don’t Account for it

I looked at some of the other Q&A here and didn't see a duplicate of this one (e.g., How can I figure out what's slowly eating my HD space? and other linked and related questions).

Finder reports that my 500 GB drive is using 499.248 GB.

OmniDiskSweeper reports a bit more than 358.64 GB once it seems to have settled to final values:

Users          287.2 GB
Applications    26.2
Developer       16.4
Library         10.9
private          6.2
lost+found       4.1
MSI              3.6
System           3.5
usr              0.4977
Google Earth.app 0.0461
others, less than .1    
Total          358.7438 GB

(I got this by running sudo open OmniDiskSweeper.app, which gave the same result as running it without the sudo. It is reporting on hidden files.)

I also ran GrandPerspective on the ~Users folder, and it accounted for only 266 GB, which is 21.1 GB short of what OmniDiskSweeper reports. (By the way, GrandPerspective version 1.5.1 doesn't seem to be able to scan the whole disk, only folders. I htought I used it to scan the whole disk in the past.)

So, by OmniDiskSweeper's account, I have about 140 GB unaccounted for. Are there any other tools that might tell me where the rest is, or why it is tagged as used?

UPDATE

I ran Disk Utility Verify and the results reported are

Verifying volume “MacbookPro3”
Checking file system
Performing live verification.
Checking Journaled HFS Plus volume.
Checking extents overflow file.
Checking catalog file.
Checking multi-linked files.
Checking catalog hierarchy.
Checking extended attributes file.
Checking volume bitmap.
Checking volume information.
The volume MacbookPro3 appears to be OK.

I don't do this often, but I think I would have expected a report of something wrong, which I would then fix by running Repair. It looks like there is nothing to do here.

UPDATE 2

df -h output:

Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/disk0s2   465Gi  464Gi  490Mi   100%    /
devfs          185Ki  185Ki    0Bi   100%    /dev
map -hosts       0Bi    0Bi    0Bi   100%    /net
map auto_home    0Bi    0Bi    0Bi   100%    /home

df output:

Filesystem    512-blocks      Used Available Capacity  Mounted on
/dev/disk0s2   975093952 973576656   1005296   100%    /
devfs                370       370         0   100%    /dev
map -hosts             0         0         0   100%    /net
map auto_home          0         0         0   100%    /home

I looked in /Volumes for MobileBackups. There is no folder (or volume) there by that name. But there is a folder with my disk volume name, "MacbookPro3". I tried to get it's size with Finder. Information says it's an alias, so I imagine it's a link. When I look at information for what is in it, some of the big items (Applications, Developer, Library, MSI, System, and Users) add up to about 113 GB of usage, but is that real? If it is, then this might be the problem but I'm guessing I'm looking at linked folders.

Storage under About This Mac shows all disk space, 498.73 GB, allocated to "other". Everything else is literally "Zero KB".

UPDATE 3
I restore from Time Machine to a 750 GB drive using the most current backup. Looking at utilization on the new drive showed that it was consistent with the OmniDiskSweeper report above.

I then tried restoring to a virgin 500 GB drive and received the message that there was not enough room on the 500 GB drive.

I backed up the 750 GB drive to Time Machine, then successfully restored that backup to the 500 GB drive. The utilization on the 500 GB drive is consistent with the OmniDiskSweeper report above.

So both Time Machine and the laptop OS were confused about what the actual utilization was, overstating it by 120 to 135 GB. But Time machine was able to restore without including the lost disk space. But somehow Time Machine had the lost disk space in its backup records as space used, so when it tested a new drive for adequate space, it got it wrong.

I'm not sure what happened, but it looks like I was able to get it cleared up in a very round-about way. I have reclaimed over 120 – 135 GB of drive space.