Probably some debris in there causing a channel for the leak. Once you get it off, make sure to clean all the surfaces including the tank glass before putting the bulkhead back on (that if it or the tank is not cracked).
I ran 10 T5 bulbs over my old tank that was 48 long x 30 wide x 20 tall. Grew a lot of beautiful sps in that tank. You should be fine with 8 bulbs. Get a quality light.
Thanks. You may be the only one who thinks so. Lol. S4 mini, but I'm using an app called photowonder to get closer shots with it. They come out pixilated, but it's a phone so not much else can be done.