Van,
Pop off your door panel and get a look inside. Sounds like you need to clean and lubricate the entire latch system.
You may need to adjust the end links as there is just enough wear in them that they won't trigger the unlock from the key hole. There is really no adjustment to that, so I assume you have 20 plus years of dust and crud in there.
If you are not planning on painting the car any time soon, any penetrating oil will work. If you are planning some paint work soon, use only WD40, and stay away from any silicone based lube as it will soak into the fiberglass panel and give you a fit with fresh paint. Use brake cleaner or electric parts contact cleaner to get the old crud out, and be mindful not to get excess on the paint or it will damage the paint. You can follow up with Lithium lube (white grease spray) when it is all cleaned out. Stick an air hose in there too and blast it after you get some cleaning fluid worked in.
