I read that Pat Buchanan wanted to be the ambassador to South Africa. Was it for the sake of helping maintain apartheid?
Buchanan was a supporter of Apartheid, which is no surprise given his white supremacist political views. The ADL for example describes him as "increasingly advanc[ing] an anti-Semitic, racist, and anti-immigrant ideology" with views "identical to those of self-declared "white nationalists."
According to Buchanan, the ambassador position was offered to him for various places, among them South Africa. He was interested because of "the whole apartheid thing". At least in that interview, he doesn't go into more detail. But given his views, there is no reason to believe he wanted to do anything else than support apartheid as ambassador.
As mentioned in the comments, according to Joe Klein, Buchanan is more explicit in his book:
He writes that he wanted to be named ambassador to South Africa by President Ford so he could support the apartheid government.