The line behind the side cover is an easy and very doable project. The line is tapped into the rear cam bearing and bleeds some oil pressure from the galley and feeds it to the head, where it is then fed to the rocker assembly. Very very common for this line to get clogged up over the years.
To remove, first remove any rings on your fingers and disconnect the battery. Why, because one of the bolts is near the solenoid and it is very easy to short out a tool onto the solenoid and your hand or rings and you can get burned really badly. How do I know this, a couple of years ago I was in a rush and forgot to do both and darn near burned my finger off. Three operations and skin grafts. I have the photos to prove it. 40 some years of always removing jewelry and disconnecting the battery and wham.
Next, remove the bolts holding the side plate. A couple of them can be a speck challenging but you can get them. Depending on how your distributor is mounted, you should be able to remove the side plate without removing the distributor.
Next, disconnect the steel line, and clean it out really well. if you have a little compressed air, blow a little air in the upper fitting on the head. If you hear air in the valve cover, the passage is clear. Reinstall the line. Wipe the block mating surface nice and clean. Take a look at the side plate, any dimples where the bolts go, or any dents, straighten them out. Install a new gasket, cork or the orange rubber version that is available. I usually like to use just a little rtv or permetex No. 3. Tighten the bolts evenly, no gorilla work here. Otherwise you will split the gasket or push it out or otherwise cause a leak. Firm and secure but not tightened to death.
You are done!
