Even though you may be diligent about swabing your instrument, wiping off fingerprints and polishing keys, you probably aren't getting everything clean. All of the keys need to be removed every couple of years to clean inside of the tone-holes, especially the hard to reach undercut which is at the base of the tone-hole (where dust, lint and saliva collect). This should be done every 2 - 3 years for most instruments.
Oiling keys shouldn't be just adding new oil to the old, nor just by applying to keys while the instrument is assembled. Old oil should be removed from the screws (rods & pivots) as well as the inside of the keys before new oil is applied.
After a good cleaning, the bumpers (cork, leather or Teflon) may need to be replaced if worn or missing. Adjustment screws will definitely need to be turned when these are changed.
Cracks might happen but they do not put an end to your instrument's life! It is always best to discover them early while they are short and not too wide. The smaller they are, the less pins that will need to be installed and therefore the repair will look nicer and be less expensive.