[Legbreaker]

In Going Home, it's stated the 2nd Marines have equipment and personnel from seven different nationalites amongst it's ranks and it's implied these were picked up during or after the offensive.
I believe the 2nd was tasked with the area from Gdansk eastward almost to Elblag (their orders were to launch amphibious assault onthe Polish Baltic Coast and across the Vistula estuary). It is conceivable that small numbers of Germans, Canadians, and Danes were attached to the division as liason units (likely Intelligence, MP, that sort of thing), and absorbed into the division once it was realised the XI Corp was cut off and they couldn't return to the home units.

A lack of ammunition doesn't ring true to me as one of the factors of the 2nd Marine situation. It is stated in Going Home that this division actualy gained strength as a result of the offensive. Whatever it was that caused them to be so crippled as to withdraw back westward, had to have been relatively big, but temporary in nature - fuel seems to be the only thing that fits.

In addition to the loss of the actual fuel carried aboard the ship(s), perhaps the bulk of the divisions stills were also lost? This would allow them to regain some measure of mobility once replacements have been constructed, a process which is likely to have taken several weeks since they would need to acquire the necessary materials first.

As for the rest of your comments, I'll post something on them in the next day or two. They're good points and need some serious thought...