I've gone through 3-4 of these over the years and I don't use them full time. They are junk and break or leak.
I have one with the newer lid, but it hasn't leaked on me. If you've already tried silone grease on the ring I'm not sure there is much you can do. Try not to over tighten, that might help.
On my main tank I bought a kit from Avast marine.......it's easy to assemble and will last your whole life. It's worth the extra cost beleive me. Use the on site coupon code and get 10% off.
The MR5 is what I have--
https://avastmarine.com/collections/...ia-reactor-kit