Roll pins are made similar to a spring in that they are tempered but not hardened. Ideally they are a few thousandths of an inch smaller than the hole so their springyness ( new word ) holds them from slipping out. Normally they should last longer than yours did but any extra strain or binding can bring a failure as Tlowe points out regarding an oil pump problem. How does the gear teeth look on the distib? Any excessive wear pattern that might indicate a high loading from the oil pump?
Solid pins like a dowel pin are generally hardened and mostly used for alignment of parts rather than as a fastener for assembly because they offer no tension to keep themself in place like a roll pin does.
Like so many other things there can be differences in quality of roll pins depending where they were made. Be nice if after you checked things out you didn't find any problems with the oil pump and could blame it on a 2nd quality roll pin.
