Using the inflation calculator, $260 in 1948 is the equivalent of $2522.64 in 2014. These were high-end machines, and built to last - no "planned obsolescence" here.
Try loosening up the solidified oil by warming up the mechanism with a blow-dryer.
The 15-91 was my first machine, and I have a fondness for it that hasn't faded even after all the other models I've seen and tried. Great for free motion quilting. It's solid, reliable and forgiving of just about anything you put under the foot.
Rewiring is easier than you think.