Both of your threads lack one thing, more details.
To check if engine is seized , put in gear and try spinning rear wheels. Might want to take plug out. Make sure no dirt will fall into plug hole.
No matter what, you'll have to pull the clutch cover. If oil is reasonably fresh, lay it on left side. If not just drain it.
At this point you'll have to figure out what's broke. Look for pieces laying in that area. Start with the starter gear/mechanism and work your way forward inspecting everything.
You might be able to save the gasket. No matter what clean gasket surface with brake cleaner or paint thinner or similar. In this case I would use permatex #2 non hardening, but any kind of silicone will work.
A Clymers repair manual or the pdf manual on the forum is needed.
Also the assembly video by Ken O'Connor will help.
If you have more questions, post back up. Please include more info.
