They have dominated.

McLean has prepared 22 group one winners for Weir from the Ballarat-based trainer’s Warrnambool stables.

Last year Weir trained an Australia record 491 winners, many out of his Warrnambool satellite stable.

The pair shot to prominence in 2015 with Prince Of Penzance’s famous win in the Melbourne Cup.

That triumph made jockey Michelle Payne the first woman to ride the Melbourne Cup winner, inspiring a soon-to-be-released movie.

Weir and McLean’s association dates back long before that success.

In 2006 the pair was involved in a long-running inquiry centered around the scratching of galloper Glebe Run on the final day of Warrnambool’s May Racing Carnival.

After more than three months, the inquiry was over in minutes when stewards announced they were not going to lay charges against Weir.

"It's a huge relief, this has dragged on for far too long (but) I knew I hadn't done anything wrong," Weir said after the stewards' findings had sunk in.

"It should have been sorted out a long time ago. It would have stopped a lot of racecourse rumours, I'm tipping."

The outcome was not so satisfactory for McLean, whose evidence during the inquiry was, according to the stewards, at the very least contradictory.

McLean was later fined $7500 on two charges of giving false evidence.

It was at McLean's stables at Yangery, just west of Warrnambool, that Weir stabled some of his horses during that May carnival, including Glebe Run.

The galloper was the favourite and on his way to the start for a class four handicap on the Thursday of the carnival when it was announced the five-year-old was a late withdrawal by order of the stewards.

Weir had already won three races for the day, with Real Assay, Himstedt and Virvacity, and if Glebe Run had been successful, he would have collected the trainer's prize of an $85,000 Mercedes wagon offered by the Warrnambool Racing Club.

The drama at Warrnambool unfolded after steward Bradley Dunn and racecourse detective Jim Monaghan inspected McLean's stables about 11.30am that day.

Dunn and Monaghan discovered stomach tubing equipment and packets of powder used for drenching horses hidden under wood shavings in two of the boxes at the stables.

Stomach tubing of horses, although not illegal, is not allowed less than 24 hours before a race.

McLean initially denied any knowledge of the stomach tubing equipment that Weir claimed he had hidden because he did not want to get McLean into trouble: he had seen the stewards approaching and believed they would jump to the wrong conclusions.

During further questioning at the races that afternoon, McLean changed his story, telling stewards he had seen the equipment and Weir with a bucket containing a reddish liquid but had not seen Weir using it.

It was a result of the change in McLean's evidence that stewards ordered the withdrawal of Glebe Run.

Weir had nine runners on the day and seven of them were pre-race or post-race tested. All samples, including those taken from Glebe Run, were negative.

Racing Victoria chief steward Des Gleeson said the two versions of what had happened at McLean's stables on May 3 proved McLean to be a "singularly unreliable witness".

But the troubles for McLean were far from over.

On July 24, 2008,  McLean was fined another $8000 and given a suspended sentence after being found guilty of an elevated TCO2 charge.

The elevated TCO2 reading was detected in a sample taken from Jerrymac prior to him running fifth to Bolle in the Mercedes-Benz Open Hcp (1400m) at Warrnambool on May 1 that year.

A TCO2 level at a concentration greater than 36 millimoles per litre of plasma is illegal.

The Racing Appeals and Disciplinary Board issued McLean a 28-day licence suspension but suspended that ban until July 31, 2010.

In December last year McLean received a six-week suspension.

McLean was suspended after making false or misleading statements over where Trap For Fools was stabled before the Coongy Handicap at Caulfield on October 20.

A race-day inspection found Trap For Fools at Weir’s Warrnambool stables and not at McLean’s Yangery complex.

Trap For Fools went on to give McLean his first group one victory, taking out the McKinnon Stakes on the last day of the Flemington carnival.

Weir's first group one winner was with She's Archie in the 2002 SAJC South Australian Oaks before running second in the 2003 Melbourne Cup behind champion Makybe Diva.

He was a horse breaker, a farrier, a knockabout journeyman with a reputation as a horse whisperer.

Such is Weir’s success that he’s inspired a catch cry from punters: “Back Weir, drink beer.”

That success is now under the microscope.