What's the resistance spec for a distributor's carbon "button"?

I have a needy '83 400i that I'm rehabbing. It has a 4.8 liter 4-cam with a single distributor and the cylinder heads with the intake ports between the cam covers, like the 365 GTC4. I would like to know the correct spec, in ohms, for the resistance of the center post in the distributor. The assembly that I'm testing includes the brass female plug in the center of the distributor cap, where the coil wire attaches, and the spring and carbon button combo located in the inside of the distributor cap. One of my multimeters gives me a reading of 10.3 ohms, and another fluctuates between 12.5 to 13.9 ohms.

Also, if I needed to replace that spring-button assembly, where would I go for the part? Are there any interchanges with Marelli caps for other brands?

 

Hi John. This is a point of interest because I am seeing a persistent arcing from the tower of my ignition coil to the coil's negative post. The thought is that, if the resistance is too high at the distributor, the voltage is finding a less resistant path to ground by jumping from the inside of the coil tower, through the insulating plastic molding, to the negative post. I'm no Edison or Tesla, but it's a theory.