Another failure I had was two of the bed support lugs sheared off the 360 y-bearings: -
These are under more load on my machine because I have a heavy metal bed. They also get some strain when parts are being removed from it. Rather than strip the machine down and replace the y-bearings, I made a new part that sits between the two y-bearings and supports the bed on three rather than four points.
If the bed is slightly flexible, for example when made from Dibond, then all four corners can be levelled independently. When it is stiffer, for example 6mm aluminium, then you can only adjust three points independently. In fact, one of those can be fixed and then there are only two points that need adjusting.
I made this using the support material option of Skienforge for the first time. To use it I have to enable the raft module but then disable the raft by setting the base layers and interface layers to zero. Without the cross hatch option the support material is easier to remove, but it tends to come away from the bed. For raft-less support the first layer of the support could do with being solid.
Other persistent problems I have are connectors losing contact, so reseating them once a month is good idea. The constant vibration and heat cycling seems to make connectors unreliable. Screw terminals with ferrules over the wire end seems to be the way to go.
The M8 nuts on the frame shake loose, I wish I had used lock washers! Also the grub screw in the pulleys eventually work loose after months and the one in the extruder drive gear needs tightening after a few weeks. It seems to be impossible to keep anything tight in plastic, especially when it is oscillating backwards and forwards. The plastic gives a little and that movement causes screws to work loose. Perhaps some thread-lock in the set screws would do the trick, but I am not certain that the screw might need to be tightened to take up slack caused by the plastic creeping.
Of course running a machine 24/7 is not what most users will do, so it will take many months of normal use before these types of fault manifest.