Introduced in 1999 as a replacement for the Eagle Vision, the 300M hit the American market to mixed reviews. On one side of the debate were those who said that a front-drive, V-6 sedan was by no means deserving of the "300" name. On the other side were folks like the editors of Motor Trend, who named it Car of the Year in 1999. The 300M remains as popular on the used car market as it was new, owing partly to a lucky stroke of engine choice.
Unlike its LH-platform siblings the Concorde, LHS and Dodge Intrepid, the 300M came with only the 3.5-liter version of Chrysler's overhead-cam V-6 engine. While it was related to the 2.7-liter offered in those other LH cars, the 3.5-liter wasn't known to have had the design flaw that made early 2.7-liter engines such notorious oil-sludge machines. Full-synthetic oil is a kind of unofficial requirement for 2.7-liter engines, as cheap oil tends to cook solid, turn into sludge and clog the engine's oil galleries. The 3.5-liter doesn't have that problem -- or so they say.
While the 3.5-liter is undoubtedly a better engine, it's interesting to note that many auto parts retailers recommend not just the standard, Chrysler-spec 5W-30 oil, but a very specific formulation of synthetic-blend oil with additives designed to prevent sludge buildup. AutoZone in particular recommends the store-brand 5W-30 GF-4/SM Motor Oil, with Castrol GTX (which also contains specific anti-sludge additives) and a number of other synthetic blends being the name-brand buyer preferences. That's an interesting indicator that, in this case, 6 quarts of prevention might be worth a thousand pounds of cure.