Of course SA (SA?) is right to say that there might be more to the current problems than were anticipated in Marx's analyses of those of the 1850s and 1860s. And no doubt there are a lot of would-be Marxists who deal with his word as holy writ. But what makes Marx different is not any one or other concept, but his method, which is unique, and wholly misunderstood by most economists and not a few Marxists. Its basic elements are that social forms (the 'economy' is just one) are dynamic, and changing, not just in their proportions (higher prices, lower prices) but in their categories (rents replaced by profits, markets by planning and so on).
SA's separation of the 'constants' and the 'variables', then, is particularly deluded. There are no constants in social organisation. You cannot push off the constants over there, and look at the variables over here, change is taking place throughout. You notice it at the end point of the process, when something happens. What? Some banks are over-extended? They why of how that happened is what needs to be explained. How it was that the world was awash with surplus capital looking for an outlet is the preceding question.