Is it a:
A plastic vacuum pump resovoir in an automobile?
The bigger I am, the less I will hold. No one else would be so bold.
Two interpretations: (i) A bigger vacuum has less stuff in it. (ii) As tight seals stretch out, they don't hold as well.
I get comfy in the car, as we travel real far.
They're used to power/control automotive parts and accessories.
I used to get used a whole lot. Now, nobody gives a squat.
They're not in as common use as they once were. (?)
It's clear when I fail, you'll hear folks wail.
Some of the components that they can be used for include brakes, door locks, and ventilation systems, giving people reason to wail.
I was popular in the eighties. I sure miss my Mercedes.
Mercedes are well-known for these systems.