Thank you Rafa, great and thoroughly clear post in the Articles Forum.
I had just been messing with an HP-97 card-reader the day before I got to your article, and thanks to dried gummy marmalade-like stuff in the worm gear, my "clutch" had given up, too.
My solution was probably a bit more drastic than yours: after cleaning all parts in alcohol, I punched out the remaining plastic fragments inside the aluminum sleeve of my clutch, filled it with clear RTV silicone, and slid it onto the motor, then pushed the worm gear home... a bit of positioning and it seems to work just fine, but only time will tell if it has longevity and adequate "give". Your fix Rafa, with the cling-wrap, seems very sensible. Wish I'd thought of that...
My card-reader appears to be a little strange. The little nylon balls and single nylon roller-wheel have mysteriously gone quite rough and porous; I can scratch powder off them with my fingernail. Never seen nylon DO this before. I may have to change them out soon, though for now they will still work marginally. Katie W. has said the balls are available from SmallParts.com; I may have to lathe a new little wheel myself, though.
For the rubber capstan, I epoxied on a small piece of latex surgical tubing. I had not intended to glue it at all, but the "tire" sometimes stalled on the moving shaft as a card met it. I am waiting for the epoxy to finish its set right now, in fact.
For assembly: I put the balls and wheel on the one side of the sandwich, cut a strip of paper a bit less wide than a mag-strip and wrapped it around the ball-laden carriage-piece, securing the ends on the other side of the piece with tape. Then on the other side of the sandwich, I installed the springs. I laid the piece with the balls in it on top and snapped them together, then cut off the tape and slid the paper out from between. I wonder how they did this at the factory?
Repairing the mag-card reader seems to be the initiation, the rite of passage that HP users must go through. This is my first; I just got the '97 a few days ago and thanks to the articles on this site, I think I shall now have an operable machine and figure I can learn 67/97 programming. (I think a nametag or badge that looks like a mag-card, with the MoHPC logo, would be a fun memento for the gift shop, Dave...) :-D