alemmons

iTrader: (14)

Is there any reason I should order the gasket rather than using some RTV or a cereal box (I know there are some people around here old enough or cheap enough to have done this.)

SA3R

Cereal box type will absorb & hold moisture between firewall and booster over time.
Silicone does a similar thing but has acetic acid in it, and will cause similar problems down the line.

Use a sheet of proper gasket material or use polyurethane body bonding cement ('Sikaflex').

(Yes I've used cereal box method of gasketing back when I was 16 & poor as dirt... never ended well in the long term.)

DaleClark

iTrader: (55)

Do it once, do it right. This isn't something that's easy to get to, I would get the correct part and take care of it so you're not back in there down the road.

That gasket can't be THAT expensive.

Dale

IRPerformance

iTrader: (41)

Agree. Just buy it from Malloy Mazda.