I've mentioned before, but I used to have a SUV with the GM 3.2 V6. This iteration of the engine had very small oil drainback holes. When there was a little carbon buildup on the holes, it didn't allow oil to drain quick enough and would burn oil. It would burn about a quart every 3000 miles.
Found a forum that suggested Seafoam to clean the carbon buildup on the drains. I'll be darned if it didn't work great. It cleaned the engine, solved my oil burning issues.
Granted, my engine had 70K miles... not 210K miles. I'd be awful nervous about causing bigger issues...