Vac Leak on the brakes

[Tom Mandera <tsm1@domain.elided>]

I might have been right on the leak around the mating surface.. I don't 
know.. I slathered clear RTV over it last night.. and it still leaks.. so 
I look around it some more and put my finger along the seam here and 
there and listen...

Seam isn't leaking now (was it ever?  I could've been mistaken).. 

Instead, what's leaking, is what appears to be a horizontal (from pass to 
driver side, across the truck) *bolt hole*.  This hole is just in front 
of the booster and below the m/c.  I can't say with certainty at the 
moment on *which* part it belongs.. but it's there.  It looks just like a 
spot to thread... oh.. a 1/4" bolt through with a nut and a head on 
either side.

Put my fingers on both sides of this hole, and I feel the vacuum, and the 
engine idle RPMs pick up.

I looked at my brand new m/c and booster (for the '72) to try and 
determine which part "owns" this hole.. neither of the new parts have 
this... hole and flashing.

It appears to simply be a smooth bore hole, below the m/c, between the 
m/c and booster, and slightly in front of the booster.  Like I said, the 
hole is horizontal.. parallel to the ground and parallel to the front bumper.

Any idea why this is there?  Suggestions on plugging it?

If I don't hear a better idea before long (are there rubber plugs for 
this purpose?) I may opt for a 1/4" bolt of appropriate length, and lots 
of clear RTV silicone sealant on the bolt head and nut and just seal it 
up like that.. 

-Tom Mandera, Helena MT