You are using a three foot power bar? Have had them release with a sudden snap on some engines. (not mercedes) . Never got to the point of considering if a pipe should be added to the power bar or perhaps a good impact tool might be better. They should come. If you eventually get them out check the threads very carefully and measure them to see if they have been seriously stretched before reusing them. I do not like the ideal of taking the heads off the bolts on the chance the threads have rusted in the block. not much of a possibility but.