From this description, you can see a VFD is essentially little more than a computer and a power supply. Keep it dry. Keep the connections tight. Let's look at each of these. It contributes to a lack of airflow, resulting in diminished performance from heat sinks and circulating fans.
Dust absorbs moisture, which also plays a role in failure.
Periodically spraying air through the heat sink fan is a good PM measure. However, although discharging compressed air into a VFD is a viable option in some environments, typical plant air contains oil and water. To use compressed air for cooling, you must use dry, oil-free air or you're likely to do more harm than good. This, in turn, requires a specialized, dedicated, and expensive air supply. Common plastics are prime generators of static electricity.