It was made in Germany, so that limits the years of manufucture.
Door 1.Philadelphia and the number has to do with what it was used for and by whom.
Door 2. The container contained a product made in Germany and shipped to Phialdelphia.
He thinks it may be an early 1960s late 50s synthetic oil or chemical can. 30L equates to almost 8 gallons. And would make sense as Germany was almost all synthetic oils, chemicals and such during the later years of the war