I don't know how to repair it, if its not working. It is a diaphragm so if it breaks or becomes hard I don't know who can rebuild it, maybe someone who rebuilds vacuum advance units.

Your wiper switch is starts the wipers by pulling down and adjusting the speed by turning or rotating the knob.

The side plates with the grind mark or raised lump,are used in only one side of the shackle.
Which is the side of the hex with the star washer. Supposedly the threads on that side plate has a binding thread.

The rear spring shackle part between the threaded bushing and the side plates was no.316476 cork seals. I would replace them with rubber o rings as you can get almost any thickness and diameter you will need. The side plates next to the hex of the head of the bolt either have a notch ground in later ones or a raised lump earlier ones.

On 1935 to 1937 and maybe 38 and further. They used a felt wick on the firewall side of pedal pivots base. Pull the pedal away from the firewall or have someone depress the pedal fully, to see the oiling wick at the base or pivot point of the pedal.

Packard electric was originally part of Packard car company but was sold off to General Motors sometime in the 1930,s ,maybe to get more operating capital? Just for info about the electric part, for those who didn't know.

What carb are you using,a Stromberg? The way you have the safety wire will tend to open or richen if there is any flexing of the vacuum line,that it is tied to. The original factory carb was CHandler-Groves or later known as Holley.The original factory replacement was WA1 Carter. Even though the C-G carb was said to be bad,I have known two 115C owners who used the C-G carb with no problems.

Its a wheel cyl. pin. They used 2 per wheel cylinder. I doubt it is from your car, if your brakes are working well. Probably a spare part.

In overdrive you will get that sensation.

If you need the CYL. ventilator outlet tube,it is the same for all 120C,115C,1600 1,1A,1D,2, 1700 1,1A,2 1800 1,1A 1900 1,1A engines part no.333934 Superceded by 315430
Anyone selling a parts engine would probably sell you one or Kanters or Max Meritt or any of the parts venders.