Good idea, I’ll try Teflon tonight. If i silicon without the gasket, do both sides correct?
Personally I'd try the teflon tape first, just to see if it helps seal those threads under the nut. If it does, then try replacing the teflon tape with a little silicone on the threads instead. (Or not, if you're happy with the teflon tape!)
I'd keep the gaskets as designed. On my Synergy Reef v2 overflow the gaskets between the outside box and the tank glass act as a nice thin spacer between them.

