Transmission Leak--Very Specific Question
 

I have a 722.418 transmission. I have finally isolated my leak. Just above the pan, just under the cooling line, on the left side of the transmission just behind the bell housing, there is some sort of a plug about the size of a half dollar that takes a 14mm Allen wrench. This is the source of the leak...it appears to be fully tightened.

What is this? Can it be easily resealed? What do I need to do? Is there any risk?

Thanks for any help/advice anyone can provide.

the plug itself doesn't have a seal, but inside there is a part with o-rings that get brittle over time. are you certain it isn't the modulator valve just above?