Yeah my 1st failed attempt involved a hobby knife on the seems as well. It was just too beaten up in the long run to be stable when reconstructed. Opening the crotch are is easy on most those but hard on that bc I was trying to "save the belt" but it holds the crotch piece in place.
Aaah, dr. Midnight is probably the hardest one I've ever done, I have about 3 in pieces. Just be Patient and keep prying a bit at a time. Cutting along the seams with a hobby knife would make it a lot easier.
I've done it tons of times with varying degrees of damage. The bigger built bodies (Batman, Hawkman, John Stewart, Dr. midnite) Can be pretty difficult, what I do is drill four small holes. Two on the shoulders near the neck and two under his armpits. Pry slowly and work my way around to each of the holes. Be firm but not too firm and you should get that nice crack sound. You'll need to fill the gaps in once you put the body back together though.
Dang was gonna offer you a fee to install some Copperhead arms and legs in a Dr Midnight torso until I saw you lived in the UK!