What is the recommended oil change interval on a [DSM]?

Most people will operate their DSM under one or more conditions deemed "severe" by the manufacturer. For severe (typical) operating conditions, oil changes are recommended each 3 months / 4800 km / 3000 miles.

Non-severe conditions: 
For 1G turbo models, oil changes are recommended each 6 months / 8000 km / 5000 miles. For 1G NT models, oil changes are recommended each 12 months / 12,000 km / 7500 miles. For 2G turbo models, oil changes are recommended each 6 months / 8000 km / 5000 miles. For 2G NT models, oil changes are recommended each 6 months / 12,000 km / 7500 miles.

The proper oil weight depends on the temperatures the car is driven in. For 1Gs, both NT and T models can use 10W-30 between -23 and +50 degrees C (-10 to +120 degF). 5W-30 can be used for lower temperatures. 1G cars hold 3.9L (1.8L engine) or 4.4L (2.0L NT and T engines); the oil filter holds about 0.4L, and the oil cooler (if present) 0.3L.

Some owners recommend you change the oil twice as often as required, or use synthetic oil and change at recommended intervals. There is no proof that this treatment extends service life.

The Last Word: Face it, the car is getting old. Unless you're a fanatic, the recommended intervals is probably fine.