I usually shoot at apertures between ƒ-8 and ƒ-11, avoiding ƒ-16 and ƒ-22 when possible. When shooting 400 speed film is is rarely necessary to go larger than ƒ-8 or ƒ-5.6.
Basically, I try to stay away from smaller ƒ-numbers to prevent narrow DOF problems and I try to avoid larger ƒ-numbers to prevent diffraction around the aperture blades.
The lens LOOKS clear around the edges. Although the camera is 55 years old, it is in good condition. It was stored in its original box with original packaging, additionally stored inside a military ammo box with the lid sealed shut. The ammo box was kept in the back of a closet in an upstairs bedroom of the house. This is probably as close to ideal as the average person can get. No?
Unless there is something wrong with the camera that the average person can't easily detect, I'm pretty sure that it works as well, today, as it did when it was new. I have only put five rolls of film through the camera and have had very few problems at all. Counting the times I've used it, I can't imagine the thing has been fed more than a dozen rolls of film in its lifetime.
The only thing wrong with it is that the meter doesn't read correctly. It works but reads a couple of stops low but, since I can't count on the error to be linear, I can't say, for instance, that the meter always reads N-stops low, etc. Instead, I just use a handheld. This is par for the course, given the camera's age. I don't see any reason to spend money repairing the meter unless there is something else wrong with it. At this point, I don't know for sure. As much as I would love to send the camera in for cleaning and calibration, I don't have the money to spend right now.
If I could prove that there was something on the camera that needed to be fixed, I could see fit to give a higher priority to repairing it.
What's a good way to test the camera? Run a roll of film through it, taking pictures of things like a picket fence from known distances, with different combinations of shutter and aperture then analyze the resulting negatives?