In my experience it varies wildly in how reliable something is and how much work has to be put into it. From all the different kind of stuff I have worked with the most unreliable equipment was usually the new stuff that is packed with all sorts of electronics and sensors. If you have a high quality machine build back in the days of the GDR maintenance is usually not really needed (except lubricating from time to time).

We once had a robot that was so god damn unreliable, that in the end it was a 5 digit number in reparations just to keep it going. Nothing ever worked and the contractor who sold and maintained it was A completely incompetent shithead. In the end we were able to repair most of the stuff ourselves, but we rarely went a single week without someone having to come and fix something. It also exclusively broke down on the weekends or IB The middle of the night, where its extra expensive for someone to come out. Eventually we threw it out and went to a different brand and now everything works like a charm. No random breakdowns in the middle of the night and the whole system us much more refined.