What are some common aileron failures?
When talking about that sort of thing, you're really looking for single-point-of-failure weak links that are difficult to detect during a walkaround or inspection.  Hinges don't normally just let go with no warning.  They get loose and sloppy first.  Same with bellcrank bearings, rod ends, and pulley bearings.  Things in general on airplanes can get really loose and sloppy and still work because there are large fudge factor margins built into the design (like, a crack on a piano hinge might have to progress to 80% across it before normal loads would make it break).

If you're talking about "aileron failure" as in "spontaneous complete loss of aileron control", this is an extremely rare event.  If you had to pick something, you'd generally look for items that can just degrade with no obvious signs and then suddenly let go.  On the typical single-loop cable run control system you'll find in a Cessna or similar, that weak link is the control cable itself, at swages and where the cable bends to go around pulleys, or from corrosion.  The check for cable degradation, besides visual inspection, is to wrap a rag around the cable and pull it along feeling for wire snags (or you can use your bare hands if you enjoy the potential for surprise searing pain).

For cable corrosion, it can seem attractive to go with stainless cable, but stainless cable is weaker and SS doesn't like to rub against itself and the cable tends to fret and break down at pulley bends (why aircraft SS cable has a lubricant in it - the identical-looking SS cable you get at the hardware store doesn't).  In the transport world and in GA I think, you will find mostly galvanized carbon steel cable, which is stronger and doesn't break down as readily (the zinc is a very effective inter-strand lubricant, as well as corrosion preventative).

In terms of overall wear and tear, generally it's parts with moving bearing surfaces that see concentrated loads.  The aileron hinge closest to the control rod will always get loose and sloppy first.  The bearings in the bellcrank in front of the aileron where the bearings are under a constant radial pre-load from cable tension, on top of flight loads.  Pulley bearings at 90 degree bends where radial loads are high.  Pulleys and bearings oriented horizontally go bad sooner than vertical ones because the oil component of the grease in the bearing leaks out over time and the bearing rots out.

In the end though, most of the degradation isn't wear and tear, it's degradation from lack of use.  Like cars, airplanes do not do well sitting stationary for long periods, especially outside.