Hi,

The apparatus itself has to be held in a certain direction as if it was mounted.
There is a bobble weight inside that engages if it is slung or tilted suddenly like in a sudden stop or definitely in an impact.
It doesn’t take much for it to engage and it has to jiggled sometimes under normal usage of pulling the strap. The car’s movement locks and unlocks it more times than not, but you never notice it.

I assume you have not taken them apart especially the coiled up spring thats under the cover. You don’t want to let the “Jack” out of the box! You can open it carefully but don’t let the spring get up.

You should be able to rotate the whole assembly to hear a or feel a slight clunk of the bobble weight moving.
It’s not much as it only toggles or engages a ratchet paw to a toothed wheel.
Maybe … you need to blow out the mechanism. That is unless it has rusted as they have only a flash coating of chrome or cadmium. I haven’t seen what happens the snow belt cars.

As far as locating newer ones I do not think Volvo changed their winder design over the many years.
Unless the cover in the lower Pilar changed to fit under the plastic interior trim, there should be no need no problem getting one from other cars.

When I snagged my spares I went for the passenger side units to get around that.
What you have to watch out for is changes in the buckle that fits into the console as Volvo kept doing different notch configurations through the years to fit their console. In the last years of the 240s separate button releases were bolted in to the floor. Again changes are minuscule but bite you in getting replacements.
The belt webbing on the rear seats are definitely a different length.

It’s the belts web material is what shows wears and that is of course on the driver side.
A newly painted car needs a nice belt to go with it. 👀
All aging has to be a concern if you think out there to the the extremes of safety.
The webbing stuff was meant to stays strong for a long time for a couple hundred pounds of a sudden stop jerk. I meant that for the force not the for the jerk in front of you 😳

It is probably over engineered as the width was needed to spread any pressures out across the bodies contact surfaces during restraints.
I have seen where people even put fabric accessory sleeves on them for their shoulders no matter the make of the cars.
A real long thin one might work cosmetically but it’s not going to roll up nicely through the guide at the top. It has enough problems with twists and drag.

There might be someone that applies new webbing and can stitch it properly but I never heard of any.
That might be in another posted thread or a search engine job.

Phil