Annually check the inverter for loose screws and terminal connections. See the attached picture for an example of a loose connection causing high heat and discoloration of the lugs.
Inspect the DC Bus Capacitors for leakage, ruptures, expansion of the protective capacitor cans. If noted, replace the capacitors.
Inspect the soft charge resistor for discoloration due to excessive heat. If so, the soft charge contactor and contact may not be functioning correctly.

Semi-annually check the cooling fans for proper operation.
Quarterly clean the inverter of dirt, dust, and debris. See the attached picture for a dirty heat sink.

With an F7 inverter constant U1-40 will tell you the elapsed cooling fan operation time. If it exceeds 20,000 hours replace the cooling fans.

The following parts are rated for these times.

Cooling fans are rated for 20,000 hours or 2-3 years
DC Bus Capacitors are rated for about 5 years
DC Bus Fuse are rated for about 10 years.
Printed Circuit Boards are rated for about 5 years.
This is all based on average ambient temperatures of 86F/30C
Load Factor of about 80%
and Operating Time of about 12 hours per day.