[C10wip]

I think it has a protective function. There's the obvious seal on the firewall on the right hand side in the picture, but what I was worried about was the sliding part in the booster. If you operate the brakes with boot off, you'll see that there is a sleeve which moves in and out of the booster body and looks to be a fairly close fit. My concern was that if dirt and whatever built up on the sleeve it could damage the booster or cause that sleeve to bind up. Also, I didn't want crud getting into the booster and around the booster rod.
But I think if you could patch it up it would still do the job - or if you find a place where you can buy one let us know what the part number is.

I also just finished replacing a $50 ignition coil on a riding mower because a mouse chewed the spark wire off of it, and just before that a set of plug wires on my car. Not happy with mice.

btw - I grew up in Oakville, but moved the US around about the time my truck was made ( total coincidence ).