I took one apart after breaking the needle shaft.
They're not hard to take apart and reassemble, but I understand from Jim Carter's speedo rebuild guy that restoring the magnetism isn't that easy. Get it wrong and it won't work or will indicate a totally incorrect speed. Re-decalling (notice the word I just invented?) is probably within the capabilities of the average shade tree mechanic, but getting the speedo to indicate the correct speed may not be without some special skills/training. I get the idea that remagnetizing them is a closely guarded secret.
I wound up buying a remanned speedo.
