Bob,

I *think* I get the picture from how you describe it.  My
understanding is that the flare of a double-flare is pretty
flat to start out with (though it rounds a little when the
nut is tightened) while the bubble-flare starts off more
rounded and may crush and weaken if the nut is tightened
into the wrong fitting.  Given that, I provide the following
ASCII art for fun and entertainment.  I take it this is
double-flare arrangement:

              Section through brake line fitting

//////////////////////////////|
//////////Master Cylinder/////|             _
/////_________________________| ___________| |
////(                          (           | |<--Brake line nut
///( |<--flare                (            | |
__(  |_______________________(-------------| |__________
            brake line
__    _______________________                 _________
//(  |                       (-------------| |
///( |                        (            | |
////(_________________________ (___________|_|
//////////////////////////////|
//////////////////////////////|

At any rate, I did consider changing master cylinders on my
bus.  As it turns out, I have two (late) 67s with the dual
system and one (early) 67 with the single system.  I bought
a new master cylinder for my Deluxe and a rebuild kit for
the Westy (the line broke when I pulled it off for the
rebuild).

Will keep an eye out (chameleon) for leakage.

Thanks.

-Jim Bryant