I have a 2007 2500 4x4 with the 5.9 & 48RE auto trans, 218K miles. Bought in Phoenix in 2015 at 197K miles from 1st owner. Now in IL, noticed when we brought it back from AR, it was leaking trans fluid enough that it used 2 gas home. Since then, uses a at every 100-300 miles. Pulled the Tran last Feb, as all indicators showed a leak from the frt pump seal. When pulled, seal was perfect. When pan was dropped, was pristine, no cluch material,, showed evidence of a rebuild, upgraded servo pistons, colored springs in the valve body, non--OEM frt band. Put New square cut O ring and frt pump seal in, changed out the pressure transducer as suggested. The leak continues, but am isolating over time. Leak is much heavier on the RH side, have checked all the pressure check plugs found none loose. Did the UV check with the full bottle today. Cover plate & torque converter are dry. Front pump is dry. There is a heat exchanger you can just see on the rear LH side, the trans lines go to it, what is it's purpose ?? Running out of ideas....O ring on the cooling line, porous case...?? Ideas ??

 

How about the dipstick tube grommet thingy? Where it enters the pan.

Also, the heat exchanger up above is a oil to water heat exchanger for trans oil.

Chay

 

Yes, I did forget, was changed out last month, no change....used (2) FelPro pan gaskets since. I did the UV check yesterday, really not conclusive, still RH side of trans, no smoking guns. I am looking at the main body to tail extension, when I rebuilt earlier 518s, did have issues where the gasket had a thin section that will walk if not secured with Permatex #2. The oil cooler really isn't a factor right now. Thx for the idea though....