The price sounds very reasonable to me. I would have no problems using the Amsoil for engine oil, but use genuine MB on the other stuff. People have favorable reports using other stuff, but the "genuine" MB transmission fluid IS formulated for your transmission and there is NO substitute for MB power steering fluid (would probably be a good time to change it as well, but MB's PS fluid has anti-foaming additives that keep the foaming down at the higher pressures the MB system works at). I have a 98 ML320 that just turned 130K with no major issues. I do have a little more oil consumption than I would like, but the amount used is not terrible and it actually improved over the first year I owned it (bought 4 years ago with 69K on the clock).

Also, not all issues for the 98 were dealt with under warranty necessarily. The front sway bar hangers were changed later from a bronze bushing mount that got noisy whenever it wore enough to get slack to a rubber-isolated mount system. Its worth upgrading if yours is noisy, clunky going over bumps at low speeds. The lower ball joints should be checked out as well, they don't seem to last long though they will still go quite a while even with wear (they cause a creaking sound going over bumps at low speed). Ball joint R/R runs about $250 per joint at a shop. The fuel filter may or may not have been upgraded to the new style. I honestly have been running the old one and haven't changed it out yet because it is a mother to get to and it hasn't been giving me issues. I thought it was flaring up last year with a few hard starts, which turned out to be the original battery dying.