This has nothing to do with 'clean' engine oil or dealer service. Dealers NEVER inspect the vacuum system for cracks, they just wait for codes to develop and then throw parts at it until it goes away.

In most instances, a small vacuum leak leads to a rich running system which then fouls the plugs and O2 sensors, and ultimately the CAT. The P0133 is generated by the REAR O2 sensor trying to get the injectors to change their rate of flow and get the front O2 sensor to respond to the problem.
EDIT: It might even be a dirty MAF sensor or MAP sensor.

But, if the elbow to the vacuum line at cylinder #1 is cracked or some other air enters the intake manifold, the engine management will over spray the injectors and make it rich to counteract a lean condition.

Unless your CAT is making rattling sounds, it is probably OK.

A P0420-428 is a sign that the CAT is about to expire.