Mine get a complete tear down based on the use. Some more than others. My main commuter was a Raleigh 3sp Sports. In 24 years it has had 2 complete overhauls and is overdue for one right now. I have a 20 year old Giant Excursion that has only been ridden maybe 500 miles and is nowhere near ready for an overhaul. I have a brand new Redline 9.2.5 that I am going to tear down this weekend, because I don't think they used enough quality grease in it at the factory

I do my own work as much as possible. It seems no matter what I pay someone to do I usually end up having to redo it myself to get it done right. So I just save the time, money and agravation and do it myself the first time....just takes a bit longer for me to get around to it.
Aaron