I had some real battles with my unit as well. Teflon tape has always been my fav but this time would not do the trick for me. All of my leaks were from the threaded connections (all the tube slips were OK). I resolved the leaks by using the brush on thread seal with teflon (available in plumbing supply). Only issue I have now is I over tightened one of the fittings on a DI unit and it has a hairline crack in the blue cap that had to be epoxied
I also found my flow was way to low using the supplied pierce connector, switched to a true ice maker fitting. My unit is about 6 feet away from the supply so I also T-ed the supply and ran 1/2" line right to the unit.
Next step will be to put on a heat tape on the supply and insulate it as the town supply here is quite cold. The warmer the supply, the better the output.
Francis