I had similar issues with my Subal D800 housing. In addition to the problem you're describing I also had issues with other buttons depressing when the camera was at depth which crippled the camera - for instance I couldn't review images or change the focus position. After several trips back and forth to Backscatter it's now all sorted out and works fine. A bit frustrating that it took that much effort but I'm happily shooting now.
Same thing happened to me. It seems like it was designed to be pressure fit with a bit of sticky tape to give more grip. So I removed the expired tape put in some 2 sided sticky tape on the black plastic barrel of the lens itself and slid the zoom ring back on. Works fine. Never really felt the need to send it back in.
My guess is that the zoom gear wasn't designed for the stresses of having a zoom gear added (also by pressure fit which exerts lateral pressure on the ring). That and the additional torque from the gear probably loosens the ring over time.
Point Lobos is the safer option in some ways - you can usually dive there even if the weather isn't cooperating whereas the boats have to go around the peninsula from Monterey to dive Carmel and if it's windy you'll end up staying on the Monterey side. I dive on the Escapade but the boats are all fine.
If you dive Point Lobos be sure to swim far enough north before dropping down. The southern part of Whaler's Cove is shallow and usually has pretty bad vis. As you get past Cannery Point (the bluff next to the parking lot) it starts to get deeper, you get reef and the vis typically improves dramatically.
Central California is always a bit hit and miss from a conditions standpoint but there are ways to maximize your chances. Visibility is nearly always significantly better in Carmel than in Monterey. Shore diving Carmel is best done with some local knowledge so a local buddy or a guide from one of the local shops is a good idea. Probably your best option is Point Lobos State Reserve. You need a buddy to dive there per the park regulations so if you don't have one you might think about hiring a guide. You also need reservations since they limit the number of divers per day. This usually isn't an issue for weekdays but you need them well in advance for weekends. The local dive boats mostly dive only on the weekends but they are also a good way to get to the better dive spots both in Monterey and Carmel.