If snugging it doesn't help, take it apart, get it nice and clean, confirm no cracks in the fitting or the boss/adapter/tank, then coat the threads with teflon pipe sealant...the brush-on kind. Reassemble, getting it as tight as comfortable without going ape on it, then let it set overnite before refilling and putting heat & pressure into the system. If you can't afford to let it sit and cure, use teflon tape, instead.
Still no joy, it might be time to have a shop redo that fitting's main seal at the tank, or...replace the whole thing if it's in bad shape, etc.
I actually got 1/8th of a turn on them both and with everything cold and 14psi on the pressure tester they are not seeping at all.
Secondary - I have a TINY seep coming pretty sure from the timing cover to block interface above the crank sensor - those bolts did not turn at all. Leaving pressure on overnight see how much it drops.