The good news is that, since October 4, not a single CTA bus has broken down while I was aboard (and yes, I have been riding buses, not every day but often).
The less good news is that this morning a minor fire (or at least smoke) aboard Purple Line Run 503 delayed inbound service 20 minutes during the AM peak. The problem was aboard a 3200-series car, CTA’s newest. I don’t know the specific details of the fire, perhaps it was unavoidable, but it doesn’t seem to be due to the age of the equipment.