My diagnostics order......
1] Plastic sleeve on the Nader pin. If you pin won't budge, a quick rap with a hammer will usually loosen then. Use a long handled ratchet or bar to break it loose.
2] Worn hinge pins. Find them in the HELP section at any parts store. Easy to do.
3] The "butta" tool.
Aligns and tweaks the hinges after replacing the hinges or hinge pins. I used mine all of 5-10 seconds, but was well worth it.