Nut shim... please look at the first pic, Ken. Doesn't it look like there's a veneer of some sort at the bottom of the nut?
Also, look at the second picture. At the B string side, the nut is about 1 mm inside from the edge of the fingerboard (sorry, can't explain that any better in English..) On the C string side the edge of the nut is perfectly aligned with the edge of the fingerboard. So looks like someone messed with the nut and sanded 1 mm off that side of the nut (???). I already imagined the bass didn't left the factory that way 30 years ago...
Anyway, if I was in the States, even on the Pacific Coast, I wouldn't wait a minute to send the bass to you. But shipping costs from Europe to the States have gone crazy, not to mention the mess with customs..
Is purchasing a new nut from you a possibility? I have a local luthier/repairman which is pretty good and I would trust him replacing the nut.