Newbie here. Just a thought. I have no experience restoring str8s, but I have restored many fountain pens and we use heat to break stubborn joints loose all the time. Not enough heat to melt the plastic, just enough to beak the bond, 135F or so. Because you are dealing with steel, you can use more heat than we do and still be far below a temp that would ruin the temper (I think. How hot can you get the blade without affecting the temper?)

The trick with pen restorations is to heat up the joint slowly, at low temp, try to take the joint apart, if it doesn't budge, heat it some more and repeat. Pens usually come apart in a minute or two, but I've had pens that take 30 to 45 minutes of careful heating before it just pops apart.

My thought with your str8 is to heat up water in a pan big enough to immerse the blade. Heat the water to a safe temperature, say 150F. Hold the blade in the water with your hand for a minute or two, remove from the water and try to remove the blade with your fingers. Repeat until the blade falls out. Or just heat the frame, leaving the blade out of the water. You want the frame and blade to expand at different rates to break the bond.

Rubber gloves will help your grip and allow you to use hotter water. The key is how hot is too hot? I think anything below boiling should be safe for the temper, but don't know for sure.

I've used this technique many times on pens - plastic, hard rubber, and metals. It works well. I don't think it would affect the temper, but I do not know for sure. Maybe you can modify this technique to be str8 friendly.

Hope this helps.

Dave