Maybe I can be of more help;

A common symptom of high mileage cars among "many" others of course, are Worn Piston Rings. There a a few techniques to determine if this is the problem.

Piston Rings seal the Pistons against the cylinder walls to create a near air tight seal. This will allow the cylinders to produce compression (more important in diesels) during the "compassion stroke". With out adequate compression and engine will have blow-by, burn oil, and smoke and lose power or not run at all. Other problems can however cause the same symptoms such as worn value guides and or valve seats, indicating a need for a valve job. Rings require an engine tear down, valves send the head out to a shop.

While doing a compression test measure each cylinder and compare it to factory spec and look for a problem cylinder. Squirt a bit of oil into the problem cylinder and retest. A temporary rise in compression pressure will indicate worn rings. If there is no change, then valves are the most likely cause, then cracked rings, etc....... Of course you can never be sure until you pull the motor apart. In aviation we normally will put a bore scope into the cylinder to have a little look-see before doing anything.

Hope that helps a little.