I bought a 2004 Mazda 6 with 140Ks, it got a good reading on the emissions test, but I have to add a quart of oil each week. There is no blue or white smoke coming from the exhaust except when I have the RPMs near the red line I do get some blue smoke. Will it need the engine rebuilt?
Start with an oil change or maybe even two. If the maintenance had been ignored previously, there could be sludge buildup that is restricting the oil flow from the cylinder head back down to the oil pan. That will cause oil to build up on top where it can overload the valve seals and work its way into the combustion chamber. You'll see black soot on the inside of the tail pipe.
Another method is to add a small bottle of dye to the oil. After driving it for a day or so, search with a black light. The dye will show up as bright yellow stains. Be sure to check the tail pipe again.
From your description it sounds like valve guide seals or stuck piston rings. Rings can become stuck when the engine has been sitting for a long time. They will usually free up after a while. Valve guide seals can often be replaced without removing the cylinder head from the engine, but a lot of import engines require oddball specialty tools that must be bolted onto the head after it has been removed.
If the engine is running well, there's no need to think about a total rebuild.