I have a ST .45 and the idle stop screw is missing as well after
a few flights. Runs just fine without it and without any silicone
so I figure why fix somthing that isnt broken.

I would say just buy a new ST .75 they are $109.99 on Tower
Hobbies. I would venture to say a complete carb kit is almost
$50.00 if you put all of the parts together. So cost the same
but something to be said about a brand new engine out of the
box.