Last owner apparently not a big fan of changing the oil

I'd just put some deisel oil in it as the normaly oil you run. In time it will clean a lot of that up. Also beat on it on occasionIt will loosen up curd and get more oil up top.
For the sucking sound - look at the carburetor bolts (famous for loosening on slantys) and any vacuum hoses. If your car has AC or power brakes check those parts too.