Some searches come together very nicely while others take forever. This is one of those ones that worked out very well and it took not quite a minute from the time the medal arrived in the mail to me speaking to the soldier's widow.
43114 SGT Algimantas Stanaslovas Leonavicius was born in Germany then emigrated to Australia. He served in the SASR during the conflict in Borneo known as the Confrontation. The only lead I could get on Algimantas was to his name on a RSL honour board in South Australia.
Due to the unusual surname I took a punt that there wouldn't be many relatives listed in the White Pages. Sure enough there is only one person by this name in SA so I called and ended up speaking to Algimantas' widow. He died in 2000.
Thanks to Helen and Rod who found the medal and sent it to me. The returned medal tally is now 1111.