Hi Edd,
I have found a Thomas Filer on the Waterloo Medal Roll*as a drummer with the 1st Batt., 4th Regt. of Foot.
Thomas and his brother John were both Chelsea Pensioners and, although I have found Thomas's service records on FindMyPast, I have not found John's. However, there is a John Filer directly above Thomas's entry on the 4th Foot list of those awarded the MGSM (John has three clasps and Thomas four). I believe that there is a good chance that John is Thomas's brother and wondered if he was also at Waterloo?
*https://library.royalmintmuseum.org.uk/archive/waterloo-medal-roll?
Thanks for your kind offer to help with our research.
Best regards, Steve.