I know you are bothered mostly by the smell, but a completely plugged vent is even more serious because it could force methane and other sewer gases into the house. This could make someone very sick.

Are you in an area that is having snow and ice that may clog the vent? If so, you need to get someone up there right away and open it up. Plumbing vents are designed to just let air rise naturally and pull out the odors, there is typically no easy way to force them to vent without going up to the roof and removing any obstructions.

Bruce

If the weather is cold,try this. Fill tub and basin with hot water then watch for fog at vent stack as someone drain's both at same time while flushing toilet. Fog from stack prove's it's open and toilet wouldn't flush well if vent is stopped up. I suggest you open the clean-out cover to see exactly how your sewer smell's. I've never heard sew gas described as ".kind of like a sour eraser type smell." Odds are the odor is coming from something else and you can refocus your search.

Jimmy rig a garden hose to an extension pole and flush out the vent from a ladder? Since you cant walk on the roof easily. Normally I take hot water up on the roof and pour it down. But I can walk on my roof.