I am trying to give you as much correct information as I can, but I own just 1 car so I don't know if it is 100% correct
In attachment you have 'picture 1' that gives you an overall view of the car.
Picture 2 gives you a close up of the bolt at the tunnel seen from the passenger side.
Then you have a picture 'driver side', where you can see the 2 bolts for the retractor and female end from the front belt
The picture 'passenger side', gives you also a general view of the 2 bolts but at the passenger side.
I just describe what I have found on my car, so I am not sure that it is the whole Truth but there isn't much done at my car over all those years....
Where the retractor goes, you have the chassis then a steel washer, the carpet, the rubber washer and than the bolt.
At the tunnel, where the female end goes from the belt, you have the tunnel, steel washer, carpet and than the bolt (so no rubber washer there)
I have also purchased the AMK kit nr. F-3560 (Seat belts Front), so I can compare the old stuff with the new.
The bolts are identical, so that's 100% correct
The rubber washers (4 pieces in my kit) are a bit thicker as the originals, but that can (probably) be explained that the bolts and rubber washer has been tightend for so many years. But in the kit there are 4, in my car just 2
In the kit there are 2 kinds of steel washers :
1/ bare steel (4 pieces) : diam = 1 7/32 inch (original one is diam = 63/64 inch / the whole in the middle is exact the same (= 29/64 inch), also the thickness is the same
2/ zinc yellow plated (2 pieces) : diam = 55/64 inch (no original found on my car)
In attachment also a picture of the old and new bolts and washers.
When I look in the Osborn interior assembly manual, at page 40 (seat section) I see at sectional view BB there is a washer at the tunnel (behind the carpet) and then the bolt, so that looks correct with was done in my car, accept that the washer is described as finish phosphate and lubricant, but it was in bare steel.
When you look view DD at the same page of the Osborn manual than there is a steel washer at the chassis (that must bed phosphate and lubricant, the carpet, steel washer (in plain steel), the retractor, steel washer (in plain steel) and then the bolt.
In the manual there is no speaking of a washer in rubber....
So knowing that, we can perhaps say that the AMK kit is correct that they provide the 2 extra washers (diam 55/64 inch)?
But the finish isn't correct according the Osborn manual, but is correct with the finish of the parts that came out of my car.
I hope that this will help you a bit further, but I can't say what you must do or not.
Within a few months I have the same problem as you have now
But there are persons, like Jeff and others, that have way more experience than I have for helping us further.