Go use you old gear oil - it probably is ok and you might save your customers a few pennies and increase your profits at the same time - I just prefer to use new stuff if at all possible.
I'm afraid i don't have oil in long enough for it to get old.
Even though i buy it in 25 litre drums, with no sell by date on them
.I might add something to wikipedia later. As anyone can.......


- .