Hi Bryan,
The coating that you're refering to is cosmoline, it was used back in the day to prevent corrosion on vehicles being shipped overseas. They usually sprayed the engine bay and undercarriage.
On plastic surfaces I would use full concentration Simple Green and be gentle. On metal surfaces either Simple Green or mineral spirits should do the job. Apply the mineral spirits on to a rag first and then rub the metal surfaces. Be careful not to apply it to any plastic, rubber or painted surfaces. Wipe the area with a second rag to remove any residue. Home Depot sells mineral spirits in various concentrations.
Note: On some surfaces I have not been successful removing the cosmoline and I've just replaced the parts.
Take some before/after pics.
