Before you get rid of the Consew 18, what size thread are you using that causes the machine to jam? Also, what size needle are you using? If you are using size 207 or larger thread, you need to use a larger needle, like size 24 or 25 to sew with, or the machine will jam. If you are sewing with size 138 thread, size 21 or 22 needles will work fine. Your machine uses a needle system 135X17.
If you decide to get a new machine, I would go with the Juki. The Consew 206 (Japan made) is a good machine, but the Juki is a lot better. Either one would be an upgrade from the Consew 18.
No one lives forever, the trick is creating something that will.