TURIN, I have just rung Shell lubricants tech line (to see if they had a piece of paper on the matter) and the word from them is that as long as the oil has been stored at the correct temperature and is in-date that the additives should not separate. They did say that shaking or rotating the can before use is perfectly fine and will have no detrimental effect on the oil, so anyone that wants to can do so
For my part as I have seen frothing I'll give it a good shake this time just to eliminate any possibility of that being the cause.
She doesn't think that they have any guidance at all on how to open the metal cans, and had never been asked that question before. Guess it may be a liability thing if they give any advice.