Cockpit scuppers are the two drains in the aft end of the cockpit. Hoses from these drains exit at two holes at the bottom of the stern. If they leak, near hull speed, a wave rises at the stern and can flood the boat. The hoses must be in good shape, and double clamped at both ends. You can get to them through the lazarette, or by taking out the bulkhead at the back of the quarter berth.
A sticking door to the head also indicates rot of the wood in the mast step in the deck over the compression post and cross timber above the door. If this is the case the ceiling will look like it is oozing around the cross piece above the sliding door. There is a description of our repair in the archives. But this would be a major item to negotiate if the survey indicates it.
The toerail/hull-topsides joint is another source if leaks. The list of possible issues is long. That’s why you want a survey in your deal. (Typically, you pay for it, then negotiate the cost of repair of major items by you or the current owner out of the purchase price.)
A gate valve is the kind of valve most of us have on the outdoor water tap in our homes. You turn a round handle multiple times to move a “gate” that opens or closes off water flow. There are two on our ‘77 model, one where the sink drain goes through the hull, and the other at the engine cooling water intake. In salt water they corrode, and can fail without warning. The replacement is a ball valve that closes or opens with about a quarter turn of a lever that turns a ball with a hole in it to either align with the pipe, or block it. In fresh water for 43 years disassembly and inspection shows ours are fine. SOP on a salt water boat is to replace them. A feasible do it yourself job on the hard, (out of the water) but you have to get it exactly right. Again, the procedure is in the forum archives.
The reward is a great, seaworthy cruising boat for two to four. The Admiral and I have cruised around 9,000 miles on ours over 20 years on Lakes Erie, St. Clair, and Huron. We have cruised with four (two couples grandsons, or my brothers and Dad) for up to a week. I hope this one works out for you. Keep asking questions, we are always here to help you out.