Paul,
You mention that your grandparents are Patrick and Catherine Cassells from the Springield area and that their son was Sean. Here's what I have:
Patrick Cassels was born 9 September 1887 at Clonmor. His parents were Peter and Eliza Cassels (nee Lacy). Eliza registered the birth.
Patrick Cassels married Catherine Gorman on 27 April 1926 at Tullamore. At the time, Patrick was residing in Springfield. His occupation was labourer. Catherine was the daughter of John Gorman, a labourer. The witnesses to the marriage were Joseph Brophy and Elizabeth Brophy.
Patrick and Catherine Cassels had a son named John, who was also called Sean. I don't think there were any other children, but maybe you know differently. John was born at New Row, Edenderry, Co. Roscommonand. As far as I know, Sean and his wife had two sons. Then again, you may be able to correct me on that. :-)
You thought your grandfather was a jockey. On his son's birth certificate, Patrick's occupation is listed as groom. That gets him close to horses awyway. :-)
What I didn't have was Patrick's death record. Thank you for supplying the year. Do you know where he died?
Your grandfather was one of eight children. I'd be happy to share more information with you. You might want to email me.
Karol