I'm not too familiar with the O'Day 22 but,
it must be similar to the OD 222 in that it has a self bailing cockpit. It's possible that the hose that is connected in between the intake hose fitting under the sole near the transom, and the discharge hose fitting on the transom, could be leaking due to old age. Also, the water that you have in the stern,could be rain water that's getting in around the gunwhales. If the boat is tipped up, and no water is leaking out of the gudgeons where your rudder connects via the pintles, then there is no use bothering with them. You should be able to open a cockpit seat hatch, and look into the storage compartment and see the hose for the self bailing. You should see the water too. You need to get that water out. Then, check inside the cabin on a rainy day and see if you can find some wet or damp spots in the area of where the cabin meets the deck. Or have someone run a hose over the top of the cabin to see if it may be coming in at the mast step. Years ago, I left my metal gas tank inside the fuel compartment, and the tank rusted through. All the gas leaked out through the self bailing hose, but there was enough gas in that hose that ate right through it. I had a terrible mess in the spring along with a strong smell of gas. I no longer use metal gas tanks. Certain chemicals that are used to clean fiberglass, can eat out the caulking under the rub rail, or gunwhale. Any product that has Oxcalic Acid in it will do this, and cause leaks. I'm certain that water can come in near your bow and travel toward the stern. Check your chainplates for leaks inside the cabin near the bulkhead. see if there is any black spots on the wooden bulkhead. Chainplates are noted for leaking. These areas that I'm telling you about are the places where I found my leaks. This year I found a leak coming from one of the bolts that holds my mast hinge plate to my cabin. I got aboard my boat just as it was beginning to rain and I stared at those bolts while it was raining cats and dogs and it never leaked. When the rain let up, low and behold, drops of water started forming at the end of the bolt and it kept on leaking for five minutes. All I can think of was that the bolt hole took a while to fill up, and water just seeped around the threads of the bolt. It was a small amount of water, but who needs a wet mattress, or drops leaking on your head while you're sleeping? I fixed that problem fast after I dropped my mast temporarily to get at that bolt. These are the things that you need to check though. I hope that I was able to be of some help. good luck!