[shorod]

If you really think there's sludge in it, or some evidence points that direction, I'd start by substituting 2-3 quarts of engine oil with transmission fluid, get the engine up to operating temperature with the tranny fluid/oil combination, let the engine idle for maybe 10 minutes. Drain the oil out and replace with fresh engine oil and a filter and see if the engine sounds any better. The transmission fluid is pretty effective at dissolving sludge and cleaning out hydraulic lifters (which I'm not sure if your engine uses or not).

You should also have the compression checked on all cylinders to make sure they are all pretty close to the same.

-Rod