The run of the mill HD weatherstripping is fine. That's what I used on my 124 wagon. I didn't bother to remove the factory goop, just left it in place. Guess it depends on how OCD you are.

The black foam on the flaps was there to insure the flap completely sealed and didn't leak air when closed. At this point it's quite brittle and not very effective. Your best bet is to remove it. Otherwise it flakes off and flies out the vent in small pieces, landing on your spouse's clothes, with predictable results.

Don't understand your blower box question?

- JimY