We'll take these as examples of why most, if not all, of these cores are not "fully usable". (I did a "deal" where I was being provided "X" amount of cores in exchange for two wiper motors...)
Cylinder is not restorable. Too much rust, too much pitting. After the cylinder is acid dipped to remove all rust internally and externally (can't even read the part number for the rust and pitting on this particular one), I won't be able to grind and keep the part number, date code, etc. because of the pitting.
Brush cap. The bearing was stuck to the armiture shaft and would not release and came out of the brush cap, making the brush cap unusable, because it's a pressed in steel retainer that holds that bushing. No way to put it back in once it comes out and is stuck still on the armiture where I can't get it off, making the armiture, so far, also unusable. I hope to be able to retain use of the armiture. The brush cap is also rusted and pitted and even if I was able to salvage it and soak and blast, with paint, it's pitted. Nothing can save that, pitting is pitting. Brush caps cannot be ground down like the cylinders because of the contour of the brush cap....switch plates are the same....can't be ground. With the cylinders you at least have some area work with, brush caps and switch plates are different animals.
Bearing from the brush cap stuck onto the end of the armiture. Now, the cylinder screws on these particular cores will not come out to allow me to get the windings, pole shoes and armiture out of the motor. I've tried PB Blaster, other lubricants, MAP gas, etc. My next route? Drill them out on a drill press, but for what? Bearing will not come off the armiture, windings have broken wires inside, useless, so why am I trying to save this core?
ok you get the cylinder off it and windings and pole shoes (manage to salvage pole shoes), and now the armiture is stuck in the housing bushing....again, lubricants, MAP gas, pulling, tugging, etc. to try to save the housing and have use of it. The housing has a bushing that if I score it or pull too hard and it pops out, it renders the housing unusable. 
Brush cap is rusted, screws will not turn out on this one, what they will do is break in the housing...here we go right? Is anything usable?
If the brush caps are rusted and pitted and the switch plates are either broken from shipping too many in a box to save on shipping, or they're also pitted, you get back what you provide....a crappy pitted motor...and I have to pull windings, brushes, housings, switch plates, etc. out of my inventory. What's going to replace my inventory out of these cores?
Now let's talk time. I've had these cores for 8 months, STILL can't get them apart, am tired of messing with them, why am I going to take more hours of my time, building other motors where I was provided a fully usable core, to continue to take apart something that I know at MOST I might be able to save the housing???? It's time vs usable materials.
Let's also talk "hurt factor". You get hurt when you attempt the impossible or near impossible. Broken bits, stabbed hands, blood, sweat and a WHOLE lot of cussing.
So PLEASE I hope this helps you better understand the term "fully usable core" and why I have to be such a tyrant on receiving fully usable cores. If I get lots of motors, like these, and accept them, what are my future builds going to look like when my entire inventory is reduced to parts in this condition to start? NOTHING will make them better at the end. Rust and pitting are everyone's worst nightmare, especially mine.
Questions? Give me a call or shoot me an email 865-365-5833 or kim@passion4mopars.com
