The last two times Australia have regained The Ashes, they have done so in Perth. When it comes to deciding series, Melbourne has not been so lucky, on Boxing Day or otherwise.
Out of those 11 series, only two saw Australia retain The Ashes at the MCG: 1936/37, when Australia came from two Tests down to win the Fifth Test in Melbourne and retain the Ashes 3-2; and 1965/66, when Bob Cowper made 307, Wally Grout and Grahame Thomas played their last Tests and the Sixth Test was drawn so that Australia retained the Ashes 1-1. (Although few cricket fans noticed, since cricket's go-slo had sent them to sleep several years previously.)
It is much more common for the deciding Tests to fall around Melbourne. Australia won the 1974/75 Ashes 4-1, but even though there were two Tests at the MCG, the Third Test was a draw and England won the Sixth Test.
Since marvellous draws are the flavour of the month, that 74/75 draw is worth a mention. England batted first making 242, Australia followed with 241 to trail by 1 run on the first innings. Batting second England made 244 to leave Australia 246 to win. Australia finished on 8 for 238, 8 short of the win with Maxy Walker on 23 and Ashley Mallett on 0.