Blurring of boundaries exists in US unions too
In addition to nearly four decades of experience in the United States labour movement, including 14 successful years as international president of the powerful Service Employees International Union, Stern was on his fourth visit to South Africa, has relationships with leaders in a number of Cosatu unions and follows local union politics closely.
The parallels between Stern's union and Cosatu abound, especially in terms of politics: Cosatu and its long-standing kingmaker's alliance with the ANC is on a par with Stern and his union, which is widely credited for helping to elect President Barack Obama in 2008.
But Stern kept using the proviso "in our country" not as arrogant oneupmanship, but rather as a genuine show of humility and to illuminate tales of caution.
"Almost every day from the time I entered the labour movement in 1973, except one year, the labour movement in our country grew smaller, not stronger," he said. "We went from one in three to one in 14 [unionised compared to non-unionised workers] now."
The street-smart Stern also clearly understands that South Africans cannot stand sanctimonious foreigners telling them what they should be doing.
Most attempts to get him to comment directly on Cosatu's often tetchy political relationship with the ANC, as well as on affiliates such as the National Union of Mineworkers losing touch with their members, he preferred to steer back to his former turf (he is now at Cornell University in New York since retiring from the union in 2010).
"There was also a loss of focus in unions that the most essential ingredient of their success was members," he said.
"When unions became very successful in our country, they somewhat lost contact with their members and had much more of an orientation towards electoral politics, had much more of an orientation towards big policy debates and forgot two things: one, that all our strength came from being the voice of workers and two, we weren't going to have a bigger voice if we had less members."
The decline of US unions came as a result of weaker labour laws, bolshy bosses and globalisation, in which new industries arose in which workers were not unionised, he said.
"People didn't think maybe we should organise the workers in the new industries, maybe we need a new model of unionism ... too often we looked at our political party to rescue us."
So was it a mistake to support Obama? "The fact that 30-million Americans who are poor will get healthcare as a result of Obama's election ... is an enormous contribution to the future of our country."
But there is a general "but".
"Trust me, politicians look at union leaders as someone they want to seduce and bring along for their own wellbeing; members don't. Members want to hold labour leaders accountable; politicians want to seduce them. It can make you forget that you're really someone else's voice. You're not there because of who you are, but because of who you represent."
In answer to a question on what his advice would be to Cosatu about whether to continue its alliance with the ANC, even as a progressive Stern was pragmatic: "You can make it an ideological question. I make it a strategic question: Are the workers doing better as a result of whatever the strategy is with the ANC, or [should they] do otherwise?
"I'd say what you're now seeing on the mines with [smaller and more militant union Association of Mineworkers and Construction Union] Amcu [and] the fact that there is extremely high unemployment, issues with education and housing, is beginning to pose that question differently to when it was a liberation struggle.
"Now, it is a sort of economic, nation-building question ... I would be worried if I was the government or the union, the ANC or Cosatu that 18 years later there isn't the progress everybody had hoped for."