First of all, try typing this line at a slower pace so you don't pile so badly, and you can see more uniformly as to what the carriage is doing.  Then, see if any plastic panels or other mechanical parts seem to be catching or rubbing whenever the carriage hits this point, Judging by the dip, I'd say off hand that you might have a body piece or some other mechanical "thingy" under there that is moving the carriage every so slightly upward.  Try sliding the carriage side to side to see if, in the lower case part of the shifting, that it is free of any snags or something catching the side of the carrriage.  The only other thing I can think of, and you checked out the carriage track pretty thoroughly, but see if the rails look like they're bent in any way.  Smith Corona, Royal, and a few others, good machines that they are, use a stamped metal type rail that isn't the strongest in the industry--as opposed to machines like Olympia, which uses a much stouter railing system--more in line with their upright SG counterparts.  Try seeing if there is something either on the body or within the machinery itself impinging on the carriage travel.  I'd bet that's it.

Okay, I got it out of the jacket, and had a look under the thing. One spring was off, got that back on and it still continues with the problem. I notice that if you work the carriage back and forth using the carriage release to get the escapement out of the action, by putting a bit of downward pressure,  very little but push slightly on the carriage, it "grinds' just a bit between "30 and 45" on the carriage markings. If it means anything after working it for awhile I noticed on the "rack" the top of the gear looks like it is shiny on the very end of the teeth. IS this something? OR will this in the end wear in and work right?

Further looking and I can't see thing one without taking more apart. that I an not wiling to get into that far or deeply. Thanks for the info and I will continue to try to work at this stubborn problem.

Thanks for your help, and back to screaming at the thing.

The Aerojet.