So far none of you have it right use no dope and don't over tighten as this will only cause it to leak worse. And never use a ring that has been used once then retighten it again. I have a suggestion look to see if your tube is true round as if it isn't you will get leak, if it is solder it which is the right way compression is for weekend plumbers who are to lazy to learn how to solder. 35 yrs plumbing has taught me that do it once or do it forever.
Cut out the tubing with the two compression fittings. Longer piece of tubing. Two couplers, and a bit too much silver braze. Lots of heat from a mapp torch. Inspect with miror and flash light. Put some silver braze on a part of the fitting that got missed. No leaks, any more.
Tape the heater tape back on, wrap some black foam insulation around, and tape on with electrical tape.
Good until the next leak.
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