I just had a thought, did you ever stone your commutator on that machine, and if so did you stone your exciter armature? Long story short every time I stone my commutator I stone the exciter as well, maybe that's glazed up a little, would make sense about the higher resistance you're getting. Digital multimeters are cheap at partsource, try it yourself, welder repair guys love to charge big $$ to have a "look". Or maybe I'm not understanding what you're saying, anyways good luck, oh I just got a bunch of wiring diagrams for the old 200's if you're interested.