Originally Posted by Gary Gable
I just went under my truck with a D20 mated to a T18. I cannot reference the hole in question. I took a print of your pic and it doesn't look anything like my D20. Could you give some references like: "This hole is on the left side forward from the output about 2" or something like that? Otherwise, I'm drawing a blank.
Just went and looked at my T-18 to D20 and it doesn't look like ours hookup the same way as a TH400.
But to answer your question, that picture was taken from about 10 inches below the greasebox shifter mechanism for the D20, looking towards the rear drivers side tire and up about 60 degrees. That is the passenger side of the transmission to transfercase adapter. I believe that the bolts are supposed to go through the adapter and thread into the t-case, but if that's the case, then you're missing at least two of them as there's no bolt visible in the upper passenger side hole as well.
From where I'm sitting, it looks to me as though your front seal of the t-case is leaking, the adapter is stuck on with a max of two bolts and some sillycone, and the gear oil is finding it's way out of the adapter bore, through the silicone and out that hole. I could be wrong about which way the bolts go, maybe they go through the housing and into the adapter, but even it that's the case, and I don't believe it is, you should have the ends of the bolts visible in those holes, and those holes would be threaded as well.
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