Not trying to be a twit here, but maybe the restorer didn't put any oil in the transmission. It wouldn't be the first time someone over looked that or thought the other employee was going to take care of it. Removal of the plug and checking the texture and smell of the oil the old fashion way may yield some clues as to what's in there now.

Where Are You From? Oro, Ontario

Do You own a car built by Durant? Star F Touring

Most of our cars used the 600 weight steam gear oil. Snyders.com or Macs.com who sell Model T parts also sells this gear oil others do too. I get mine from Mac's.

Where Are You From? Oviedo, Florida

Do You own a car built by Durant? 1928 Durant Model 65 4 door sedan

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Where Are You From? Iowa

Do You own a car built by Durant? yes