How Often Should I Change My Engine Oil If It Sits Parked

1985 Chrysler Fifth Avenue. Electronic Spark Control updating.
2020 Toyota Tundra TRD Sport. Shakes. New Vehicle. 
1998 Chevy Truck 300k miles Ignition System Failure. Burns Oil.
Volkswagen Passat Gurgles Under The Dash.
Air In Coolant. 
2017 GMC Yukon No Start No Crank.
2016 6.7 Ford Diesel. Fluid Changes. 
Relocating a Plugged Evap Vent System.
Headers on a 2013 Toyota Tundra.