If you're concerned about sludge, try one of the commercial "engine flush" products just before changing the oil, but don't drive it while the flushing product is in there. Just run the engine at a fast idle for the reccomended time, which is usually 10-15 minutes, then drain the oil while it's hot. You could use the old standby flushing method, which involved adding a quart or two of kerosene to the oil and doing the warmup/drain thing. If the pan's not leaking now, and the rods aren't rattling, better leave well enough alone!
Jerry
