[Mart]

^^ The images above are not indicating a problem with the pin. They are indicating that you have too much play between the splined coupler and the pinion. It is that play that works the pin and eventually fatigues it to failure. If it was not the safety type, it would eventually break and the parts will fall out and make a noise. If that one broke, the clip will retain the parts in place.
Good tight fitting splines, and perfect alignment are crucial. Any slop or as can happen with shortened drivelines, misalignment will lead to spline wear and failed pins.
Mart.