98K on odometer. Religiously serviced by FSS (now I believe it should have been more frequent). Bought ML new in 98 and switched to synthetic (Royal Purple) after 3K miles. Switched to Mobil 1 when RP raised their prices substantially. Have noticed some sludge on oil cap when oil adds became more frequent. This service, tech said he scraped sludge out of filter with a screwdriver and noted heavy sludge on invoice. I plan to change oil myself at 2K intervals for 3-4 times to see if conditions improve. Any recommendations for do/don't do are welcome. I am aware of MB sludge lawsuit but have not yet taken any action.