Part number for bulkhead seal?

[shifty]

Almost got all my water leaks fixed except 2 in the cowl/firewall area.

Need to know if there's a OEM seal P/N for the bulkhead behind the coolant overflow - circled in red in the attached pic. Hit that thing with a hose this weekend and water poured into the floorboard. Can't find in GM's catalog.

Also ...

I'd love ideas where my last cowl/firewall leak may be. I read 50 threads around the internet leading me to patch these already (all were leaking):

• Cracked seam sealer on either side of the cowl, near hood hinges.
• Leaking cowl screw sitting above the airbox opening.
• Cowl hole over above the airbox opening (Tahoes same year have a plastic cover there).
• Checked the antenna grommet, it's prefectly good as you see...

If I run a little water inside the cowl, I leak behind the blower motor. It's almost like the seam sealer around the airbox opening itself is cracked? I can't see in there though.