Hopefully you get to read this before drilling. I do
remember reading that the vacuum bleed valve
is internally adjustable. I can't find the website
but I think the top will come off if the screw are
removed and a means of adjusting it might be
found. Just in case you want to do some more
reading first here are sites with in depth discussions:
www.mercedesdismantlers.com
www.continentalimports.com/ser_ic20242.html
or www.babcox.com/editorial/ic/ic20242.htm
If you need another valve in the event the operation
is not a success I have a few from the junkyard
I can send. (I'm out of town til 4-7) Hopefully
I said something you didn't already know.