The 3662 dash pot is there to slow down the motion of the milkman. The correct lubricant forms a seal between the piston and the cylinder wall. There is a small hole in the end of the cylinder that lets air in and out. With a tight seal, the air is forced out and allowed in slowly and the milkman slowly opens the door, gently sets the can on the platform then slowly goes back into the car.
Without a seal in the pot, the man zooms out, launches a can across the platform and zooms back into the car. This is the action of the 3462 027 car and is why the milk cans for that car have magnets in the bottom, so they'll stick to the platform as they are thrown out of the car.
You want a lubricant thicker than oil but thinner than automotive grease. I used some black moly grease from Woodland Scenics (part of their Hob-E-Lube line). I don't recall needing to thin it. Using a finger, I smeared a very thin layer on the inside of the cylinder and on the outside of the piston. The before and after difference in operation of the car was AMAZING.
Good luck!
