The following code letters are applicable to the different front diff
housings available:
ADH
ACU
AHU
AHT
AKH
AKF
ANB
ANC
AOM
AOL
AAM
AHB
ALM
ALN

There is no ADK. You probably misread the ADH one.

Derek Drew wrote:
>
> SDP emailed back to me saying they have no record of ever having produced an
> ADK series front differential!!
>
> ADK is the one I have with front diff lock, and I am about ready to install
> it.
> Is there anybody with a European microfiche (mine is rather old and probably
> out of date) who can tell me what the ADKs series front diffs were? Or do I
> have some weird one-off made in the Volkswagen factory?
>