I'm so glad you posted this question and will be following this thread, for sure. I have posted several times about my smelly featherweight. I have tried many, many things in the case itself but I won't get into that here since you were asking about the machine. My featherweight machine also smells. Definitely change the oil pad, however that did not help my machine. I have washed her down with Simple Green and another product called Odo-Ban that somebody from this board recommended to me. It does help a bit but the smell always returns. So, I wish you luck. :)

I put fresh coffee grounds in my featherweight case and it absorbed all odors then I tosed it away. Worked great for me.

Pads for 301 at SEW Classic but currently out of stock. you might want to call them though as sometimes they have it in stock but have not updated the site. but for me, i just buy felt pad from Joanne's or Michael's and make my own.

I would use craft felt unless you can find 100% wool felt which is more absorbant. The felt underneath in the drip pan was made to catch all the drips of old oil and that can get pretty smelly. The ones on top are probably fine.

Oh! Do NOT go using a drill on something. I don't know who has that on their blog but that's not likely something you need to do and you could damage your lovely machine. My 500 had a stuck cam too. Just give it some oil and let it work while you are avoiding the smell for a couple days. That might be all you need to do to get it to loosen up and let go of the cam.

I agree - I've made all of my drip pads from felt.

Just to give everyone an update on what I have done so far and how it has worked. I have cleaned the outside of the machine with the Simple Green it's better but not great. I have also changed the felt and that really has decreased the odor of the mustiness substantially, I can at least go near the machine without feeling like I can't breathe. It is very evident that this machine has not been cleaned in a very long time there was so much lint in it. I am still in the process of removing it before I start oiling and lubricating anything. If I did it at this point it would just make more of a mess. Airing it out definitely was a good idea too.
I have a question I noticed while I was using the Simple Green that the light seemed to be rattling so I took it apart and there was this small piece of metal near the screw on the cap where the Singer is that fell off, is this something that I can replace or not? Also I noticed that the light looks like it needs to be replaced as it is not real bright sort of dim lighting should I just go ahead and replace the bulb now or wait till she blows out? As I said before I will post pictures of her as soon as I can and of the accessories as well. Thanks to all of you for your recommendations I really do appreciate it.

Caroline it actually isn't dried oil it looks like when a light bulb has blown out but yet it hasn't? Oh, I just thought of the perfect comparison depending I guess on how old someone may be, it looks like the old flash bulbs after you took the picture. But I really want to know about the little piece that broke off if it is necessary or not. I did read the manual but it doesn't refer to it at all, so don't know how important it may be. Do you happen to have a 401A?

Try a cat odor remover from the pet store. Spray lightly then let it dry in the sun. It has worked great on the wood cases for me. I do let them sit out in very hot sun and sometimes I have had to spray and dry for several days.