Here we go again LOL. This subject gets raised every month or so and usually sparks plenty of debate. Below are two recent threads...
https://igpmanager.com/forum-thread_2/9204
https://igpmanager.com/forum-thread_2/8088
132 days ago iGP big cheese Jack Basford commented on the subject, he said quote...
"About the realism factor, it's something people will always ask for until they actually get it, and then they will be demanding it to be rolled back. There's almost never a perfect middle ground with such features. Particularly when you put other things aside to sit down for a 2 hour race on PC, you don't want to then have your car randomly fail 1h45mins into the race. It's also demoralising when you're in a championship with friends and it maybe gets decided by something like that.
If such features are implemented to occur fairly often, a lot of thought needs to be put in to how they work. The new "reliability" attribute was the beginning of moving in that direction in the long run, but for now it's not really implemented fully. If the manager can control how random it is, then it can be enjoyable. When the manager themselves can be held accountable, e.g. because they were prioritising performance over reliability, then it is fair. It's when it's random and/or unfair that it can really spoil things."