OS X 10.6 Snow Leopard no longer mounting an external USB drive

It looks like the problem was the partition table.

$ diskutil list
/dev/disk0   # The internal hard disk
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            402.5 GB   disk0s2
   3:       Microsoft Basic Data Boot Camp               97.1 GB    disk0s3
/dev/disk3   # The external USB drive
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk3
   1:                        EFI                         209.7 MB   disk3s1
   2:       Microsoft Basic Data                         999.9 GB   disk3s2
          # ^-- Hey, that's not right!

The filesystem was intact, but the HFS+ partition on the external drive was mistakenly flagged as Microsoft Basic Data instead of Apple_HFS. I used the GPT fdisk utility to change its type back to HFS+, and it immediately appeared on the desktop and worked normally again.

I am currently experiencing a very similar issue. I ran the following command, the output of which I included. However, this still did not fix the problem for me, however maybe you will have better luck.

> fsck_hfs -rd /dev/disk1s2
** /dev/rdisk1s2
    Using cacheBlockSize=32K cacheTotalBlock=8192 cacheSize=262144K.
   Executing fsck_hfs (version diskdev_cmds-491~1).
    Journal replayed successfully or journal was empty
** Checking Journaled HFS Plus volume.
** Checking extents overflow file.
** Checking catalog file.
** Rebuilding catalog B-tree.
hfs_UNswap_BTNode: invalid node height (1)
** Rechecking volume.
** 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.
    invalid VHB attributesFile.clumpSize 
   Volume header needs minor repair
(2, 0)
   Verify Status: VIStat = 0x8000, ABTStat = 0x0000 EBTStat = 0x0000
                  CBTStat = 0x0000 CatStat = 0x00000000
** Repairing volume.
** Rechecking volume.
** 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 EXTERNAL was repaired successfully.