The hot glue is normal for those boards at those times.

You want to be checking on the other side of the board for solder joints that are cracked or looking dull instead of shiny - especially for the connector that you see in your first picture where the wire harness plugs in below the battery holder. Look at the joints on the other side of the board for that connector, and re-solder them if they look bad. Do the same with the other components BMOW mentions. Those location number/letters will be screened on the board.

For a quick fix, you can just use a hot solder iron and retouch the joints in question - let them melt and then re-harden - to see if it alters the behavior. This isn't a permanent fix,but will help you isolate the problem and tell you where you really need to remove and replace the old solder.

Many, many "dead" machines from this era have been brought back just by resoldering half a dozen joints on these boards.

If you can find the Pina book mentioned and/or the "Dead Mac Scrolls" they are extremely helpful in diagnosing and fixing these guys.