First thing to go is the fan, those last about 5-8yrs, but easy to replace with an aftermarket fan. After that, the blower, then the coils. Keep in mind that mine has no attic transfer, and everything is outside (blower, coils, etc). Its a 6 ton split unit, so gas heat, electric AC.
The main issues: salt, sand, humidity, heat.
I technically need a second unit (based on sq footage), but Id rather replace than repair, and Im not replacing 2 units.