Currently it takes 10 seconds to remove or replace a part from a vehicle.
Major parts are repaired with a 1lb 'Spare Parts' item which is consumed on use.
A Spare Parts item only heals a part by a set amount of HP which is also different for each and every part. The amount a Spare Part item heals may be also changed with ingame CBA settings.

There are 14 major parts making use of 2 ACE ones and reskins of 12 vanilla objects.
They are the following

• Wheel
  
• Track
  
• Small Piston Engine
  
• Medium Piston Engine
  
• Large Piston Engine
  
• Small Turbine Engine
  
• Large Turbine Engine
  
• Small Fueltank
  
• Large Fueltank
  
• Avionics
  
• Control Surfaces (Ailerons, Rudders, Elevators)
  
• Rotor Assembly (Heli main rotor and tail rotor)
  
• Gun FCS (Gun elevation)
  
• Turret Drive (Turret traverse)

These make use of the vanilla naming of vehicle hitpoints all based on the framework ACE had already started so I unfortunately don't feel comfortable adding much more depth here no matter how much i'd like to.

Any vehicle hitpoint not considered a Major part is classed as a Minor/Miscellaneous part and may be repaired for various amounts of the Spare Parts item. The Hull is also put into the minor category and is easier or harder to repair depending on the armor classification of the vehicle from 0 to 2.

What I want to work towards to complete the mod is Fuel Siphoning so removed we don't just outright lose the gas removed from a fuel tank and then eventually some sort of ammo handling so we can load vehicles just with the ammo we want.