Can we be held liable for a special assessment, that was levied towards the end of close, if we as seller's had no knowledge of it. We had moved out of the unit when the notification was sent out and did not receive the forwarded letter at our new address before the close of escrow.

Most likely. If you were the owner when the assessment was levied, you are responsible for the assessment.
But you get what you negotiate.
--A

If you can prove that you didn't get the notice then I don't think you would be responsible.

An agent of mine had a similar situation & we proved that the mgmnt co. had his address wrong so he wasn't getting any of the notices so he wasn't at fault for not disclosing.

The assessment is imposed on the unit & not the owner so it would be up to the new owner to sue you for not disclosing the assessment. But like I said, if you can prove you had no knowledge & weren't hiding anything then you should be ok. Consult an attorney.