Help with part # for factory tonneau (if it even exists)

This little plastic piece on the passenger rear side just snapped off when I went to close my factory tonneau cover. Any idea what this is, or where I can find a new one? It was very brittle plastic, and is currently duct taped back into place to cover the large gap it left.

Thanks in advance! The factory cover isn't close to waterproof to begin with, and this breaking certainly doesn't help.

 

ebay or dealer $22 part number
64915-04010

 

Thanks, I did some searching (should've done that first), but found this thread:

https://www.tacomaworld.com/threads/oe-tonneau-cover-p-n.493116/

Here's all of the part numbers for anyone else looking.

64915-04010 - Front Joint, RH
64916-04010 - Front Joint, LH
64917-04010 - Rear Joint, RH
64918-04010 - Rear Joint, LH