on the D12, the EGR gases coe across the top of the valve cover via a metal tube that then transitions into a silicone one. we placed a metal plug into the metal tube and welded it shut by where the 2 tubes connect. basically a piece of flat sheet about 3in square, welded onto the tube to close the opening, and then ground down around the edges to make it smooth. the EGR's will still function (opening and closing) but no gasses will be flowing over them and back into your engine. I just replaced my 1st EGR valve since doing this (it's been 19 months now) and the second one is still in there as well....hoping to get 2 years out of it!!