Your observations are similar to my own and others. You rarely see a "smoking gun" failed solder joint. Most replace the MFR due to difficulty of accessing, but many have successfully repaired. Repair is usually to clean (pull old solder off w/ solder vac) and resolder w/ new solder, ALL the joints. There not that many.

Why does the MFR fail? I rigged a bench test and measured temps of 120F or more on one of the MFR relays. It get's very hot, too hot to touch. I think this is reason for solder fatigue (joint cracking failure due to thermal stress cycling). When high temperatures combine w/ high heat output of the MFR, the joint opens and will not complete the circuit.

You can try a bench test, but I'm not sure you can simulate conditions under the dash of hot car. Perhaps by adding a hair dryer, you might simulate that condition.

Suggest repairing or replacing.

good luck

 

I'm going to desolder and resolder all of the points on the main relay just to be sure then test it by leaving it in the sun or having it in the car on a hot day with heater set to full and blasting on the lower area.

Actually I think I'm going to see if I can reproduce main relay issues by leaving it in the sun inside the car and then testing it.

For the distributor, do you think it's safe to spray brake cleaner directly into the inside of the distributor where the ICM and such are? I'm trying to see if maybe I can clean out the oil inside, drive around for a week or two and then open up the cap again and check if new oil found its way inside.

 

I don't see any harm in using brake cleaner to clean the distributor interior.

When you reassemble the distributor, be very careful pressing in the new shaft seal to avoid damage to the seal. Lube seal to reduce installation force. You should also replace the bearing. I found mine dry and loose.

good luck

 

I'm a little taken aback by how pristine the new distributor cap looks but the most glaring difference is it has no wear at all on the terminals inside of the cap.

It's obvious from the old cap that some kind of contact is occurring between the rotor and internal cap terminals. Is this at all normal? I thought the rotor transmits spark without contacting the terminals. Something tells me that it shouldn't be physically scraping the terminals.

 

They should pass very close but not touch. Cap terminals are always rough/worn. I assumed from spark contacts.

good luck