I've had those apart, too. It is getting them back together that is 'fun' you need another one there so look at... Getting that screw loose and out can be a trick. I'm sorry your repair guy didn't know what he was doing. Likely he's never seen one. I have a 401 with a bent shaft. I took the whole thing apart tried to straighten that shaft and put it back since I didn't have a donor at the time. It is still around and still bent and not working.. but it doesn't look as bent... It's sitting on a shelf in shame... Look to be sure the shaft isn't bent before you go any farther... I'm also thinking you might want to see if you can find an adjuster's manual and read it. I now have another machine that is a donor I just haven't worked up the courage to take it down another time. There are a lot of parts and they have to go back just right. I was attempting to use a Singer 500 as the donor I did get the 500 back together just fine and it moves just fine but it was the donor and the donation didn't fit.