Pretty straight forward. I changed one out on my '82 300D. I used a 10mm box end wrench, that was ground down rather thin, (otherwise you don't have room to turn the wrench to remove the four bolts to get to the pulley that Hans built, do da, do da) anyway, the four bolts closest to the engine. There is a cross over pipe you need to remove, it'll be obvious, I used a bit of sealant to hold gasket in place, be careful when torquing the pump to 24 ft. lbs. I don't think I even removed the shroud, just work around it, and the hoses. I ordered my pump from here
http://*************** or you can click on buy parts at top of page, being sure to obtain gasket, some pumps come with it.