It is a result of the elimination of the deminimus rule. You used to be able to get away without customs declarations on a lot of small shipments. Now you need that form so that they know what to charge you for the tariff. Lot of small shippers are not hip to the new system yet.

 

OK - now that I actually looked at that form - it is weird

 

I'm going with Box 8. It just isn't subject to the spirit of 591.

 

Welcome to the end of free trade and the global economy.

 

Ok, folks, Jim Davis from EB got back to me...

Due to the recent tariffs, there have been a few cases of this happening. It seems that depending on the customs official, packages are getting randomly scrutinized.

For your case, the one option that most closely relates to the kit you have is number 11.

Tick number 11's box, and fill out the rest of the document accordingly, anything that is not relevant (a lot of this document is in relation to a vehicle, and not parts) leave blank or write "N/A".

Box 11 reads:

The equipment item is subject to the Theft Prevention Standard and is marked in accordance with the requirements of 49 CFR Part 541. [591.5(k)]

Will update when I know more.
Thanks, everyone.