I've been waiting for this.
The letter from former president Thabo Mbeki to Jacob Zuma is a stinging attack on the ANC’s criticism of breakaway leader Mosiuoa “Terror” Lekota, and a critique of the “cult of personality” around Zuma himself.

The ruling party’s secretary general, Gwede Mantashe, this week quoted selectively from the letter, suggesting it amounted to a repudiation of the breakaway group that will hold its national convention in Sandton at the weekend, but the full text of the letter, which the Mail & Guardian has obtained, is more accurately described as a defence of Lekota, an implicit attack on Zuma, and a refusal to be involved in either the party’s 2009 election campaign or the internal politics of the ANC.
full story from M&G here
The story goes into some detail on the contents.

Much as expected Thabo's letter to JZ is analytical, critical and considerably less favourable to the current state of the ANC and its leadership than has been suggested by the ANC statements.

My only disappointment is that he even bothers to ask for his reputation to be protected/restored.
He then demands that Zuma “take all necessary measures” to stop party members from blaming their former president for everything they feel is wrong with the party and the *country. Zuma, he says, must remind party members that the ANC’s post-1994 legacy is based on “collective decisions” and that he must prevent them from “abandoning their democratic obligations by falsely and *dishonestly pretending that the goals of the national democratic -- revolution have been frustrated, if they have been, by one individual, Thabo Mbeki”.
Let it go, Thabo. Stick to integrity and your reputation will take care of itself.