Usually black residue on the tail pipe is not due to oil. When was the last time you changed your oxygen sensor? When a car is using oil excessively, you'll see bluish/white smoke and usually depending on when you see it you can pinpoint what needs to be fixed. If you see the smoke when accelerating, it usually means the valve guide seals are gone and getting them replaced is not difficult except for the fact that you have to take the engine head off and dissassamble it and remove the springs in order to get to them. If you get some smoke all the time it means that your piston rings are shot which probably means that your engine is low on power (low compression) and in need of a rebuild (or replacement!). I would do a compression test to have a good idea of the engine condition and start from there. As I tell anyone having one of these cars, if you are planning on keeping them and doing the work yourself get a Robert Bentley maintenance manual, it's worth it's weight in gold!