My 2000 C10 is 22-23 years old with almost 110,000 miles on it. The 2003 has over 66,000 miles.
They both start and run like new.
I do normal routine maintenance at regular intervals like oil and oil filter changes, valve adjustments, carb sync, air filter cleaning, checking brake pads, greasing shock linkage zerks, etc. just like lower mileage C10's would receive.
Just did a valve adjust and noticed some oil in a couple of the spark plug wells. That was my prompt to replace the valve cover grommets with new ones. Still on the original valve cover gasket!
Already have braided brake lines in front, but not on clutch or rear brake systems. Probably should be considering that at some point.
Winterizing (something not all bike owners have to do) is important. When properly done, it results in easy startup the following spring. My carbs haven't been off the 2000 since 15,788 miles since way back in July of 2004.
I keep a proactive eye on stuff and address things when spotted, rather than waiting for something to fail or wear out completely.
Probably over due for coolant system hose change out and its been quite a while since I replaced hydraulic fluid in brake and clutch systems.
I keep a log of all maintenance, checks and fixes with date, mileage, maintenance type and specifics of what was done. With multiple bikes and other vehicles its a must to keep everything straight and stay on top of maintenance schedules.