After building mine from scratch several years ago, I've only had to replace a broken bolt for one of the roller guide mounts. I've got maybe 500 hours on it? No idea really.
It's a pretty faithful copy of a Linn Lumber 1900 mill. The track I made much sturdier and portable and a few differences to the carriage. Everything is manual. I made my own up/down system using chains and sprockets to gear it for 4 turns to the inch. I also used hard nuts on the acme threads for up/down and I spray ATF on them every day of milling and as such don't see any galling or abnormal wear. I also use Cooks roller guides and like them. I use Kasco 4 degree blades from Cutting Edge (member here) and I can't say enough good about him or the blades he represents. I get more cuts, more consistent lumber and easier sharpening (using his cam wheel and alignment kit for the Cooks Cats Claw sharpener). My mill uses a strong running 13hp Predator engine I can't say enough good about. It feels more like 15hp, no joke. I can mill all day on a single tank of gas! Of course, my day usually don't hit 10 hours of work anymore, but nonetheless - it's economical. Ideal? Probably not - more power is better for performance, but being on a budget, I can't complain a bit.
There is always an option to add power up/down and power feed, and can be custom built. Lots of easy to access mounting points, etc. The frame is built rugged enough one could make all the hydraulic additions one could want. I'll just keep it simple for now because this is one reason I don't have any breakdowns. I'm not in business sawing so I don't need the speed or anything. Slow is good for me these days.