1989 242 DL NA (non-turbo) with functioning odometer currently showing 144k miles. Written records unavailable. Sticker on timing belt cover says timing belt changed at 92,803 in 1999.

Car has been HORRIBLY maintained, with paint peeling on roof, hood, and trunk almost to bare metal, if not bare metal. Automatic transmission fluid was chocolate brown, though tranny shifts almost flawlessly. Power steering fluid low and bottles in trunk, suggesting leak. Windshield wiper lever broken. Coolant level low. Worn tires. One wheel's lug nuts seized. Pine needle leaves present under the car and inside the engine bay/firewall area. Rear brake wheel cylinders leaking brake fluid, about 1/2 quart per week. Surprisingly, it passed California smog on the first try, oil was clean and front brakes are new/newer. The alternator looks new, too.

I want to wait another 10k miles (for 60k interval) before changing timing belt, front seals, and water pump. Given the poor maintenance history and condition of the car, is this a good idea? Do timing belts wear out after 15 years or is it more the mileage that's the wear and tear factor?