Sorry, I don't understand what you mean. sdb6 starts at 1928 sectors? 
Assuming you have either 4k or 512B hw-sector disks that shouldn't make 
a difference for alignment. If at all, I would correct it only once I 
would have full redundancy.

I think I've managed to get it back using the 4 disks I was happy
with...

quoted

offset (I have git, and have built from source before if it comes to
that... but a binary would be more helpful, or perhaps a mdadm that had
the original 2048 offset?) then clear the superblock from b and c and
re-add them to re-build the redundancy.

Well, I could probably build mdadm for you (if I should have the chroot 
matching your distribution), but can't you just download an older or a 
recent version for your distribution?

What I did was:-

wilsonjonathan@BorgCUBE:~$ git clone git://neil.brown.name/mdadm
Cloning into 'mdadm'...
remote: Counting objects: 12848, done.
remote: Compressing objects: 100% (4434/4434), done.
remote: Total 12848 (delta 9627), reused 11123 (delta 8405)
Receiving objects: 100% (12848/12848), 3.37 MiB | 184 KiB/s, done.
Resolving deltas: 100% (9627/9627), done.
wilsonjonathan@BorgCUBE:~$ cd mdadm
wilsonjonathan@BorgCUBE:~/mdadm$ make

<snip compliation stuff>

wilsonjonathan@BorgCUBE:~/mdadm$ ./mdadm --version
mdadm - v3.3-38-gb11fe74 - 03th December 2013

wilsonjonathan@BorgCUBE:~/mdadm$ sudo ./mdadm --create --assume-clean
--level=6 --raid-devices=6 --chunk=64
--data-offset=1M /dev/md5 /dev/sdd6 /dev/sde6 /dev/sdf6 /dev/sda6
missing missing
[sudo] password for wilsonjonathan: 
mdadm: /dev/sdd6 appears to be part of a raid array:
       level=raid6 devices=6 ctime=Thu Dec  5 15:33:34 2013
mdadm: /dev/sde6 appears to be part of a raid array:
       level=raid6 devices=6 ctime=Thu Dec  5 15:33:34 2013
mdadm: /dev/sdf6 appears to be part of a raid array:
       level=raid6 devices=6 ctime=Thu Dec  5 15:33:34 2013
mdadm: /dev/sda6 appears to be part of a raid array:
       level=raid6 devices=6 ctime=Thu Dec  5 15:33:34 2013
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md5 started.


Using disk manager in debian I can see md5, and the volume "md5mnt 3.8TB
ext4" as a single large partition.

I will run a fsck on it, then if thats ok will mount it read only and
have a poke around, then if thats ok will unmount it and add in the
missing drives/partitions.

Hopefully this means its all now ok *sigh of relief*

Thank you so much for your help so far on this, its been much
appreciated.

Jon.

Cheers,
Bernd