You say you want to keep your thinking within those parameters that Marx set out (albeit with some fishy sounding 'corrections' - saving the evidence like those epicycles the Ptolemaics introduced into the geocentric universe model) but not why. Marx's theoretical approach is more robust than that - it can accomodate new conditions; his theoretical reconstruction of capital accumulation is not the last word.
What you refuse to confront is that the current economic difficulties are preceded by a massive increase in the capitalist labour force. It does not really help to argue that Soviet and Chinese state-owned concerns employed more, because this was not a capitalist labour force. Nor can you write off the growth in employment in the developed world as not being surplus value producing, as if capitalists employed workers out of generosity.
You cannot avoid the problem by shuffling the time scale, nor by taking refuge in oxymoronic propositions like "slow-motion crisis". You say that capitalism has been in crisis since the late 1960s. But if that were true, the word 'crisis' would have no meaning. As Marx said, 'there are no permanent crises'. You seem to ignore the singular and remarkable annexation of the Stalinist world to capitalism in the 1990s, as if that was not an expansion.
You write about gluts. I see the opposite, shortages. In energy production, South Africa, like Britain and California, has failed to invest in the infrastructure to meet demand. World food prices rose in 2005 because of a failure to keep pace with demand. These are real questions that need to be investigated, not subordinated to a ready-made theory. 'Here is the truth, kneel here,' - that is not an attitude that Marx would endorse.