All good advice. Couple observations based on 50+ years amateur machine work.
Kroil is awesome.
Time is awesome and just be patient.
Heat and cold and mild mechanical shock help Kroil get in there.
The drill press idea is very good and works well. I use it a lot to start taps - but I manually turn the v-belt pulley at the top of the spindle. That gives me enough leverage - more than enough. It's more than one need to loosen a stuck screw. Long lever-arms and wrenches on the chuck are unnecessary and can cause damage.
Fifty-plus years ago I had a drill press with a handwheel that fit over the splined shaft at the top. Incredibly useful - never seen one since. So I use the big V-belt pulley to turn the spindle instead.
Anal-compulsive attention to turnscrew fit to the slot is absolutely important. Precision grind your tips to fit.
Very good and helpful thread!
