My guesses.

1. Possibly a vacuum leak through the brake booster or the hoses at the manifold. How about the carb throttle shafts? There should be no play in those.

2. There is definately something wrong with the brake lines at the master cylinder. Don't try to cover up the problem with sealer. They should not leak without sealer, period. Maybe the flare on the end of the hard lines has been flattened out from over tightening in the past. Otherwise, maybe the line is rusted.

3. You got me as to why! I had the same issue once after an alignment. I centered the steering wheel by adjusting at the splines at the steering box.

4. As someone else said, maybe the center driveshaft bearing or gearbox bearings.

5. Are you getting any blinking? Perhaps the flasher is bad? I once had a bad flasher that would blink the lights but not the indicator. I think that was on my 122 if I remember. The circut for a '69 140 would be similar.

6. Yes you can change the bulb. Gently pry the edges of the switch from the red face. It then pops out. Be careful with the red lense, it is pretty thin. I'll bet that the bulb in the switch is ok and it is something else though.

Good luck with the inspection.
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'60 544, '68 220S, '70 145S, '72 144E, '86 745T