According to the latest Grampians Road Report (16/12), Harrop Track is now open but has areas of erosion and is 4WD only recommended. Red Rock Road is still closed.
Coming from Halls Gap, Glenelg River Road is still closed from Mt Victory Rd so your best bet to Buandik is still probably to drive via Zumsteins/Wartook/Brimpaen to the Henty Highway. Going south and over Mirranatwa Gap and via Jensens Rd and Harrop track is probably going to take a lot longer.
Best to look at the Parks web site and correlate the road report with the map of current tracks and roads open to work out where you can drive. The current map is a few weeks old so you need the road report to see what has changed in the meantime (eg Harrop Track now open).