Primer line fitting at manifold

[rmorton]

I recently replaced my primer lines with new 1/8” copper. I had trouble soldering the fitting on the end that goes in the manifold. I used “silver solder” which actually is 95% tin. Several attempts finally seemed to stick. But now after 4 flights the line has separated from the fitting.

Is there a different fitting that can used instead of solder? All the other fitting are flared fitting with compression nuts.