Those screws are not regulation of the bleeds they only give you access
for cleaning.  They are also sometimes a source of leakage.

To remove the top screw seats try a hair dryer on hot and heat up the
paraffin before you turn.  I take a nickel and cut a notch out of the
edge to turn those seats.  I have a spare stack for parts, by the way.

D.L. Bullock
www.dougbullock.ws