This is another case where I can't publish many details to many details but the lack of details do not represent the hours of research behind this result.
15250 Joseph Francis O'Brien served in the Army Service Corps as a driver. He was 29 when he enlisted in 1917. I went down quite a few rabbit holes when I started this search due to the fact that his full name was Michael Joseph Francis O'Brien, the same as his father. It wasn't until the 1930's that he went by his full name. To cut a very long story short I can say that this branch of the O'Brien family is now extinct. It is through the family of his wife to who I will send the O'Brien's British War Medal.
Thanks to Guy T from Canada who originally sent me the medal.
The returned medal tally is now 1479.