First I would check to see if the drawband is broken. The drawband runs from the spring drum on the left rear of the machine, and runs under the carriage, connecting on the right underside of the carriage, and pulls the carriage to the left to advance it while typing. If it is broken, it can be replaced with fishing line and other materials. If it is still attached then there would be other issues to look for, but I would start with this.

I have--many times over.  One main thing to check before anything else is to see where the carriage may be binding either with the mechanicals below it or the shell around it.  Check for pinch points.  The escapement wheel should also be checked--it may have gunk in it, since it is the free-spinning design, like their uprights have, and most Remington upright typewriters beginning in 1939.  Clean it out real good, and if you have to, add a few drops of tranny fluid to grease things up a bit.  Also, the carriage track may need attention.  Take a look as to how clean or dirty it is.