i just picked up a red s4. my first s4, my s5 is, well, not going to be driven anymore, at least by me, and we will leave it at that. first, on the s4 models, is the rear diff able to be replaced with the s5 rear diff, seeings as this model doesnt have an LSD? second, is the interior door panels able to be replaced with the s5 door panels? third, the coolant filler, at the top of the thermostat housing, the part that isnt on the s5's, with the overflow hose connected to, it has 2 bolts holding it down, with a cap, and a gasket, does anyone make a block off plate for that peice, or will i have to fab up my own, and fourth, if i made my own, would that be a wise place to locate my aftermarket water temp sensor? the reason im saking before doing these simple projects is simple, murpheys law....its my life, this car is in great shape, and i dont plan on doing anything intensive to it, just fix what is broken and improve on it as much as i can without removing what stock parts are there. i just dont what to **** this up to put it bluntly.