It's difficult to be courageous enough to comment when the person asking for help says "don't bother suggesting x, y, and z." We don't know which "trick" you might have missed.

So, here are a few of my thoughts after dealing with similar issues:

- leaking timers - For several consecutive years while using the same brand which had been reliable for me, the timer would blow apart at the first "turn on." And that with the correct pressure reducer in place. Also while cautiously opening the spigot only a smidge.

My remedy was to return the item asap and ask for a replacement. Every time.

- leaking connectors - I had problems connecting plastics with metals. I now use plumber's tape at every connection.

- Always use the same brand throughout the system. A 1/4-inch tube for one brand isn't necessarily the same as a different brand's 1/4-inch. Don't know why, but it's not.

-- I found that the "ring" washers worked better than the flat style. Tired to replace them yearly (when I lived in SoCal; here, in Oregon, I change them out every several years.

If any topics not mentioned? Please specify/ask.

edit: I don't use a "hose end timer;" I only it at the spigot.