>I always thought the real intellectual differences related to Marxism were between Merleau-Ponty and Sartre, the former having introduced Sartre to Marxism and later publicly breaking with him for his "ultra-bolshevism."

Merleau-Ponty was definitely more connected to actual lived reality than Sartre was. When Marxist theory produced a horror, not paradise, he actually sort of admitted it was happening.