The Tim Leahey/Beric Lynton BMW held the lead at the halfway mark of the Hi-Tec Oils Bathurst 6 Hour at Mount Panorama.
The BMW M Coupe had been in contention for much of the early running, Lynton leading four laps earlier in the race before handing the car to Leahey after 27 laps.
The pair then moved to the head of the field following the second round of pit stops.
Nathan Morcom has also spent time in the lead, the Ford Focus RS taking control during the second hour of the race.
Trouble struck early leader Grant Sherrin when a hose worked itself loose, the pole-sitting car dropping four laps inside the opening hour of the race as the team repaired the BMW M4.
After starting 59th due to being excluded from qualifying, Karl Reindler carved his way through the field to put the CGR Performance Mitsubishi EVO X in second place before pitting to hand the car over to Andrew Richmond.
Mostert handed the car to co-driver Morcom at the car's first stop, the 2016 race winners continuing their rise through the field in an interrupted first half of the race.
Dylan Thomas then worked his way into the lead despite having to serve a pit lane penalty for a restart infringement early, only for an engine failure to see the Mitsubishi EVO X he shared with Tim Slade to roll to a halt at the Cutting.
Shortly after Thomas' car was cleared, John Bowe's Mitsubishi EVO X stopped at the same point of the circuit with a flat left-front tyre, triggering yet another safety car.
Morcom moved into the lead shortly after the safety car withdrew once Bowe's car had been cleared.
The 2016 Australian Endurance Champion moved by Jim Pollicina to take the lead, edging clear at the front of the race before the safety car emerged, prompting another round of pit stops.
Morcom pitted from the lead, handing the head of the race to Leahey in the BMW, with Nathan Antunes in the Mercedes AMG A45 he's sharing with Rod Salmon in second.
Other class leaders were Brian Walden in Class B2, Todd Hazelwood in Class C, and Josh Heath in Class D.
The opening three hours were dominated by the safety car, which was on track seven times for 32 of the race's 53 laps.