If Mr Mbeki fails, President Nelson Mandela's government could find itself in the odd position of having to stand up in a US court to defend Armscor, a principal instrument of oppression under apartheid, over "crimes" committed before President Mandela was even released from prison.
"We are being asked to take responsibility for the sins of a previous discredited regime," said an Mbeki spokesman at the weekend.
The South African government argues that America should abandon the case. But Washington insists it cannot interfere in the process of a 1991 indictment against Armscor through the US courts. PW Botha, leader of the government under which the sanctions-busting is claimed to have taken place, must be smirking at the political impasse reached by two parties he never did care for - Mr Mandela's African National Congress and the US government.
The US indictment claims that Armscor, set up in 1977 to circumvent the United Nation's arms embargo against South Africa and wholly owned by the South African government, smuggled military technology from the US in the late 1980s. Evidence of the embargo breaches turned up during the Gulf war when the US parts were allegedly discovered in South African shells which had been sold to Iraq.
Large scale arms deals between South Africa and Iraq were alleged in a 1994 court action brought by Walid Saffouri, a Palestinian businessman, for breach of contract against Armscor. He claimed South Africa had sold $4.5bn (pounds 3bn) of equipment to Saddam Hussein during the Iran-Iraq war. Shady South African arms deals also featured in the Scott inquiry, Britain's investigation into its own arms to Iraq scandal.
The US is demanding that Armscor - and therefore the Mandela government - pay more than 35m rand in compensation or agree to US surveillance of its arms facilities. Pretoria is "insulted" at the implication that it cannot be trusted to monitor Armscor's activities in the new democratic South Africa.
It has also rejected an American suggestion that it make a special plea of "no contest" in court and pay a reduced fine. Mbeki officials say this would still involve South Africa submitting to the jurisdiction of US courts.
The dispute has threatened to sour relations between the two countries. Even a direct appeal from Mr Mandela to President Bill Clinton has failed to solve the crisis. South African ministers have threatened to reveal details of clandestine deals between the US and previous South African governments if the US does not drop the Armscor case.
Ronnie Kasrils, deputy defence minister, has aired South African defence industry suspicions that the US's real motive is to keep the country out of the lucrative international arms market.