Here are the multipliers for each part , and the number of times the chance is applied on the part is represented by the (x1), (x2) or (x3)

Headlights(x2) = 1x
Windshields(x2), windows(x2) = 0.8x
battery(x3): 0.7x
Gas Tank(x1), Engine(x1), Muffler(x2) , Suspensions(x1) and Brakes(x1)= 0.6x
Radio(x2), Trunk(x1) and Tires(x3) = 0.4x
Seats(x1), Glovebox(x1), Trunk Door(x3), Doors(x3) = 0.2x

Many vehicle parts have the chances applied two or three times. (represented by the x1, x2 or x3 next to it) So the chance ends up higher than it should.
For example:
Each door could be removed, then could be damaged, and then could have its lock broken. That's three times the chance is applied.
Each tire could be removed, then could be damaged, then could have it tire pressure decreased. That's three times the chance is applied.
Each battery could be removed, then could be damaged, then could have its charge decreased. That's three times the chance is applied.

So the chance to damage/remove a door is much higher than a seat, because it's applied 3 times on the door and only once on the seat.

This also means that if you have the chance at 100, some parts will still remain.

You can tweak these values in the file "media/lua/server/Vehicles/TDCC_UpdateChances.lua" . I might make an addon mod to tweak these multipliers through sandbox settings, not sure yet.