I have a 1996 Catalina 28MKII. Removal of the panel is easy. Just take all the cushions out of the aft berth and crawl in there with your phillips screwdriver. Remove all the screws (8 or so?) and the panel is ready to remove. It's a fairly tight fit, so you'll have to sort of wiggle it out of there.
I've had my 28 for a couple seasons now, and when I got it, it had leaks everywhere. Windows, handrails, and so on. I got the little/easy leaks taken care of, and last summer I tackled the BIG leak...the steering quadrant.
Going in, I had no understanding of how the system worked, but I started with removing the panel just aft of the steering pedestal in the cockpit. That revealed the steering gear. Dirty in there, so I gave it a good scrubbing. What I discovered is that the steering gear sits in a fiberglass pan under the removable panel. At the rear of the pan, you should find a drain hole with a hose attached. The hose goes to a fitting at the stern. With this system, the water that gets past the access panel freely flows into the pan, and exits out the stern. Works great. UNLESS!!!!
Unless, like on my boat, there is a hole in the pan on it's forward end. Why would there be a hole there? Because at one time or another, someone was backing the boat (not you, of course), let go of the wheel, and pressure on the rudder caused the wheel to turn violently to either port or starboard. In the steering gear, there's a stop with rubber on it that hits the forward wall of the pan. Works just fine unless the force is too great (like in hands off backing) and the rubber covered stop punches right through the pan. Then, the pan drains into your aft berth instead of the lake/ocean. That's a wet spot we can do without.
The forward wall of the pan will be visible once you've removed the big interior panel aft of the berth. You'll be able to see pretty easily if there's a hole there. Mine had about a one in diameter hole, which I repaired with resin and fiberglass cloth. Once the hole was repaired, and I made certain the hose at the stern was firmly attached, and the system has been leak free.
While I was at it, I also removed the steering pedestal and re-bedded it with butyl tape. The boat was nearly 20 years old, and I don't want any water getting under the pedestal and going into the core of the cockpit sole (not "soul"

). The re-bedding of the pedestal project was considerably more trouble than the fixing the leak in the pan. You need to take the quadrant apart and screw around with the cable system, and get it all back in working order. All very do-able, but plenty of room for aggravation as cables slip off pulleys and get stuck and so on. Still, not a real difficult job compared to the many hellish jobs we encounter on our boats.
If you remove the deck cover just aft of the steering pedestal (and by the way, you should to clean in there), there is no reason to use any sealant when you re-install it. The system is such that whatever water flows in, just flows back out through the stern tube, so any sealant will just make it more difficult to remove the panel next time. That panel is held in by phillips head screws. I removed all the screws and filled in the screw holes in both the panel and the deck, figuring that each screw was just another invitation for water to get into the core. May have been overkill, but shy of a rollover (which I do so seldom), that panel has a good enough press fit that's it's not going anywhere.
Let us know what you find.