Skippy, the website link you provided is a Korean manufacturer site, not Chinese (and your link doesn't work because you included a full stop in the address). The reason they are refusing to provide any advice on speaker upgrades is because the site is a manufacturer site, and the page is only providing specifications of their products, it's not a "shop" page where you can buy items or get advice. They will only reply to large businesses seeking to order high volumes of their product.
https://unique-sound.co.kr/products/
Is the speaker in your VW or Audi? I guess you're looking for an alternative replacement, due to the "European manufacturer tax"? (i.e. - high parts prices).
The Chinese are your friend, they can supply the US3750B, plus they can supply a US3750C alternative. Unfortunately they provide no specifications for either buzzer, you will have to email the seller, and ask for the precise electrical specs.
However, if you check the Korean manufacturer site again, the specs are there for the US3750C they manufacture. I would presume the Chinese specs are identical, but it would pay to check.
The only problem I see, is the US3750C produces sound at a higher frequency (870Hz VS 430Hz for the US3750B) - and as you age, high frequencies are the ones your aging ears fail to pick up.
I'd suggest the major problem with your original buzzer is that it has simply weakened with age, and no longer produces sound levels to the original specifications.
https://www.aliexpress.com/item/1005010041259835.html?gatewayAdapt=4itemAdapt#nav-specification
https://www.aliexpress.com/item/1005008216109531.html#nav-specification