the cast plug directly behind the motor mount on passenger side is leaking coolant. it made no sense at first when it looked like it was coming outta the oil pan gasket, but i know that cant be right. finally figured it out by searching this forum. i was stumped until i read about the cast plugs then looked again and sure enough thats the fn leak. well im glad cause its not a big deal, other than the motor mount being in the way. if theres a will theres a way, really glad for this forum though, saved me all kinds of time. ill post pics when i go at it

 

so theres all kinds of sizes of "expansion plugs". which one do i need? is a freeze plug or not? remember its the one directly behind engine mount on passenger side. 3.9 v6 magnum if you didnt already know

 

At least you found it, now is the fun part replacing it. As for what size it sounds like it should be 1.25 since the other 2 are As Required. Remove yours and measure it or take it over and match it.

Here is the copy of the part numbers from the part manuals we got in the FAQ.
4556020 1.250
4556022 AR 1.625
4556023 AR 1.695

 

my bad, didnt read that correctly, thanks