I regularly delete old kernels leaving only the latest two entries using Synaptic.

I'm using Precise. However in my Grub "previous Linux version" menu there are quite a few entries labelled 2.6.8. I cannot find these linux-images in Synaptic.

dpkg -l | grep linux-image

Gives:

rc  linux-image-3.0.0-17-generic           3.0.0-17.30                         
    Linux kernel image for version 3.0.0 on x86/x86_64
ii  linux-image-3.2.0-27-generic           3.2.0-27.43
Linux kernel image for version 3.2.0 on 32 bit x86 SMP
ii  linux-image-3.2.0-29-generic           3.2.0-29.46
Linux kernel image for version 3.2.0 on 32 bit x86 SMP
ii  linux-image-3.4.0-030400-generic       3.4.0-030400.201205210521
Linux kernel image for version 3.4.0 on 32 bit x86 SMP
ii  linux-image-generic                    3.2.0.29.31
Generic Linux kernel image

Sudo update-grub gives:

Generating grub.cfg ...
Found linux image: /boot/vmlinuz-3.4.0-030400-generic
Found initrd image: /boot/initrd.img-3.4.0-030400-generic
Found linux image: /boot/vmlinuz-3.2.0-29-generic
Found initrd image: /boot/initrd.img-3.2.0-29-generic
Found linux image: /boot/vmlinuz-3.2.0-27-generic
Found initrd image: /boot/initrd.img-3.2.0-27-generic
Found linux image: /boot/vmlinuz-2.6.38-11-generic
Found initrd image: /boot/initrd.img-2.6.38-11-generic
Found linux image: /boot/vmlinuz-2.6.38-10-generic
Found initrd image: /boot/initrd.img-2.6.38-10-generic
Found linux image: /boot/vmlinuz-2.6.38-8-generic
Found initrd image: /boot/initrd.img-2.6.38-8-generic
Found memtest86+ image: /boot/memtest86+.bin
Found Windows Vista (loader) on /dev/sda1

sudo apt-get remove linux-image-2.6.8-8-generic gives:

E: Unable to locate package linux-image-2.6.8-8-generic
E: Couldn't find any package by regex 'linux-image-2.6.8-8-generic'

My boot folder contains the following:

abi-2.6.38-10-generic         initrd.img-3.4.0-030400-generic
abi-2.6.38-11-generic         memtest86+.bin
abi-2.6.38-8-generic          memtest86+_multiboot.bin
abi-3.2.0-27-generic          System.map-2.6.38-10-generic
abi-3.2.0-29-generic          System.map-2.6.38-11-generic
abi-3.4.0-030400-generic      System.map-2.6.38-8-generic
config-2.6.38-10-generic      System.map-3.2.0-27-generic
config-2.6.38-11-generic      System.map-3.2.0-29-generic
config-2.6.38-8-generic       System.map-3.4.0-030400-generic
config-3.2.0-27-generic       vmcoreinfo-2.6.38-10-generic
config-3.2.0-29-generic       vmcoreinfo-2.6.38-11-generic
config-3.4.0-030400-generic   vmcoreinfo-2.6.38-8-generic
extlinux                      vmlinuz-2.6.38-10-generic
grub                          vmlinuz-2.6.38-11-generic
initrd.img-2.6.38-10-generic  vmlinuz-2.6.38-8-generic
initrd.img-2.6.38-11-generic  vmlinuz-3.2.0-27-generic
initrd.img-2.6.38-8-generic   vmlinuz-3.2.0-29-generic
initrd.img-3.2.0-27-generic   vmlinuz-3.4.0-030400-generic
initrd.img-3.2.0-29-generic

and

ls -l /etc/grub.d

total 56
-rwxr-xr-x 1 root root 6715 Apr 17 20:16 00_header
-rwxr-xr-x 1 root root 5522 Oct  1  2011 05_debian_theme
-rwxr-xr-x 1 root root 7407 May 17 09:22 10_linux
-rwxr-xr-x 1 root root 6335 Apr 17 20:16 20_linux_xen
-rwxr-xr-x 1 root root 1588 May  3  2011 20_memtest86+
-rwxr-xr-x 1 root root 7603 Apr 17 20:16 30_os-prober
-rwxr-xr-x 1 root root  214 Oct  1  2011 40_custom
-rwxr-xr-x 1 root root   95 Oct  1  2011 41_custom
-rw-r--r-- 1 root root  483 Oct  1  2011 README

gdisk -l /dev/sda

yields:

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: not present


***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format.
***************************************************************

Disk /dev/sda: 312581808 sectors, 149.1 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): F832A498-05E1-4615-B5B1-757ACB4A757A
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 312581774
Partitions will be aligned on 2048-sector boundaries
Total free space is 4183661 sectors (2.0 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048        61442047   29.3 GiB    0700  Microsoft basic data
   3       163842048       169986047   2.9 GiB     8200  Linux swap
   4       169986048       312578047   68.0 GiB    0700  Microsoft basic data
   5        61444096       159666175   46.8 GiB    8300  Linux filesystem

Please help with removing the old and inexistent kernels from Grub.