Speed sensor dummy plug leaks

[dodge123]

I have a 05 2500hd 4x4 with the 4L80. Like the title says, there is a dummy plug (for a second speed sensor) above the shift cable bracket on the transmission. I guess this sensor isnt needed on this model. After changing gaskets and fluids twice due to leaks I finally noticed the o-ring seems to be leaking culprit.

 

It is a rubber ring with an orange coating on it. I tried a regular black neoprene o-ring from the hardware store but it still leaks. Im thinking the orange coating may be a leak proofing thing and possibly the diameter is very specific. I havent ordered a new one from rockauto yet. I was just wondering if anyone else has had this issue and any experience?

 

The tranny seems to be not shifting at the correct points, like holding 3rd and 4th on the upshift for longer than it should. Im guessing there may be a combination of the tranny sucking in air and the cable may need adjustment. I cant shift the truck manually into first since the last tranny gasket change so the cable is probably out of adjustment.