These types of milestones always astound me. A car is tested for 100,000 mile (exposure/shock/vibe) to qualify for sale (most countries). A motorcycle is cycled at 18,000 miles, as many motorcycles do not see extreme duration cycling or use. The expectation is it will be ridden less distance/time than a car, and its end of life comes more quickly than a car. Heavily modified decorative Ducati's in the garage or on the wall are an outlier.
For the engine to last 300,000 is in itself, remarkable, but the frame (joints, welds) also lasting that long is also remarkable. The long and short duty cycle (vibration over time) was [probably] never explored at this duration. The fact that the tabs, fasteners, and other joints are also still functioning (due to moment arm flexing) over time is also remarkable. Lastly, the plastic gears in the IP also lasting...just wow.