Erte

So I just bought a 1993 fd efini with a 13b. I'm trying to figure out the whole apex seal. I've read that a general guideline is 100k km is the replacement time line. Is that true? What causes them to go faster and or last longer? Is it an easy replacement? The car already has a few mods. A fan mod. Battery has been moved. A FC commander. Turbo timer. I don't know a whole lot when it comes to these so don't tear into me too hard.