Harold,
If you don't mind me jumping in here, (Don's a little busy right now moving and loading a half dozen semi's
) Simply use the cheapest clear silicone caulk you can find.
I usually wear a cheap plastic glove, pump a hand full of caulk on to my finger tips and from the out side of the vent hole, reach in and load up the inside lip of the opening.
Then I simply put the vent in from the outside, turn and line for the proper fitment and pull up tight to the body. That's it, AND if you ever want to change or bleed the master cylinder, it's fairly easy to just grab the vent, push and wiggle a little and it will come right out.
It is a snug fit, you should have to twist them a little to "snap" into place. A couple of test fits please, before final posistioning!
DV...sounds like another one is almost ready for the road!