An intermittent fault like that suggests a sticking hydraulic valve or a faulty electrical connection or coil. All the best, I find intermittent faults the most frustrating. You know, *n$@**andnn etcetera.
Well it would be best to catch it when it is bothering like bucko suggests. Are you getting magnatism at n1 solinoid and feed reverser solinoid. My best bet you are and that you most likely have trouble in the one way clutch on orbit motor. If this is the old spring type clutch you will need to get it torn down to check springs and get it cleaned out. Many of the old spring systems that first come out during the N days have been replaced with cog type clutch used on R machines. later feed reverser kits for N's came with cog type clutch system and might be found on some salvage machines. Spring clutches were prown to getting dirty and draging and very expensive is smoked. Cog systems perfectly trouble free. Good luck