Instead of second guessing OP's need/desire for routine maintenance on his Nikkormat FTN, why not just pass on the name of a reputable repair person. I have had good luck with Garry's Camera Repair servicing my Olympus OMs. He also services Nikkormats. The cost is very reasonable and turnaround time is quick.
The primary problem is that the same piece of the meter in Nikkormats is what fails, making cannibalization for spare parts difficult. Very rugged cameras except for that fault. Therefore it makes sense to just buy another since replacement is easier and cheaper than repair.
Luckily, I now have four Nikkormat FTN with good, stable and, accurate light meters. Three of these have no other significant defects...they just need some routine maintenance to bring them back to full status. Two of them actually have pretty decent cosmetics - a bonus.
I don’t understand the idea of the need for a camera to retain its value unless one deals in cameras. It is a tool to use. Better to think in terms of reliability.
Instead of second guessing OP's need/desire for routine maintenance on his Nikkormat FTN, why not just pass on the name of a reputable repair person. I have had good luck with Garry's Camera Repair servicing my Olympus OMs. He also services Nikkormats. The cost is very reasonable and turnaround time is quick.
The ring resistors (in Nikkormats, F & F2 finders) often clean up with "DeOxit", a soft toothbrush, and an Artgum (tan cube) or Mars plastic (white block) eraser. The meter switch located under the advance lever also gets dirty & can cause erratic readings.