dirty oil

[rahkling7]

Just bought a 2004 E320 4matic wagon which came off a lease. Oil is VERY dirty.. obviously lessee did not keep maint schedules up but I got a helluva deal on the car. Question: Aside from changing the oil and using a cheap brand and letting it run for 30 minutes and changing the oil again is there any additive anyone might suggest using to help with the cleaning process or would this be a no no? I know any sort of additive for cleaning is a no no on high mileage engines but this car has 50K miles. If I go the cheap oil route with a quickie oil change should I use a very low viscosity oil which would help the flow inside the engine? Thanks.