You can't really worry about ANYTHING like that that's happening with the machine before it's even been cleaned. You've said that the type bars seem not to be striking with enough force. Just go clean out every slot and joint between keys and segment and keep doing it till they move better. AND behind/under the segment of course. 

What's a 2" ribbon?

Kat is right. Fully clean the machine, oil only the parts that should be oiled, and then assess its performance. If the type becomes "light" with the cover on the machine, it's very possible that the spools are dragging and not allowing the ribbon to advance properly. Are they metal or plastic spools? Metal spools can become deformed, so make sure that they are perfectly flat and level; a misshaped spool can cause the intermittent print quality you're complaining about. And make sure the ribbon is correctly threaded through the machine; it was designed to work that way - bypassing certain parts of the ribbon path is never a solution.

Concerning the spools themselves, the SF was designed to use DIN 2103 spools and 13 mm (0.5 in.) ribbon. I believe that the DIN 2103 spec denotes a 54 mm (2.125 in.) spool diameter, so if you're using 2 in. spools now their size (diameter) shouldn't be the issue.

Also, if you're still having trouble with things and you've got it all cleaned up and everything, look underneath the machine and check the mechanism to see what it's doing.  There might be a wadded-up piece of paper or something gumming up the works that you didn't see topside.  Also, check for popped or missing springs--that is a common issue as well.