its not a o ring, its just a rubber grommet the hose plastic end pushes into on the booster.

get some carb cleaner, spray all injectors and vac lines, all gaskets areas, uim, the egr tubes, tb gasket, lim gaskets. aka the whole top of the engine.

if carb cleaner spray is used and it hits a leak area the idle will jump up. if you use brake cleaner the idle will drop