How old is the thread and what color is it? If it is black you might want to try a different color. I'm not pulling your leg here. My wife has on occasion, had similar problems with thread and always black. We think it has something to do with the amount of dye the fabric has to take weakening the fibers. Sounds wacko... but all the non wacko areas are covered.
You may be threading the machine wrong... but I would tend to doubt it. They usually thread rather intuitively at that age of the machine.
DRW coating on cordura could cause cause a coating. Does this happen right away? or does it take a few stitches to happen?
Second thing to look at is the threading of the bobbin. That is more likely to be misthreaded than the machine. I assume it is a vertical bobbin for that era Singer machine.
Here are bobbin directions from that era.. (not that machine)
1Hold the bobbin between the thumb and forefinger of the right hand, with the thread on top drawing from left to right. (In other words.. the thread should be pulling toward you off the top of the bobbin.)
2) With the left hand hold the bobbin case with the slot in the edge on top.
3) Pull the into the slot and under the tension spring into the slot at the end of the tension spring.
Try the bobbin fix first. Let us know what the result is. If you pics I can scan and post them.
While you're at it check and make the needle is in properly. It should have a flat index side that orients it correctly. I don't want to insult your intelligence but we've seen it happen.