Need help figuring if my engine is still useable 1987 rm250

You can skip this paragraph to get to the meat and potatoes if you wish. First off sorry for this being my first post but I recently got an 87 rm250 in trade for an 3 year old laptop. At first I thought I was kind of screwing the guy over since the computer sold for a little over $300 in it's condition but he seemed eager to trade (hindsight is 20/20). Anyways, I looked at the bike and it definately needed work but appeared to be an easy project until I started to tear it down...

I found a spot on the left crankcase right below the sproket that looks as though it was repaired with JB weld and painted to match. I don't want the laptop back and I really do want a bike to kick around on sooo.... what should I be looking for when I tear into the engine? Should I even go that far? Could this have been caused by a chain seperation? Is there positive crankcase pressure on this engine?

Thanks,

Gore

Thanks ed I guess I will have to get it running to see where I want to take it.

gore