2004 Murano head gasket problem?
 

I own 2004 murano. Recently, with 17000 transmission was replaced. Now 1500 miles later i noticed white sludge acumulating on engine oil cap. I replaced oil and have the same effect. Dealer says there is nothing wrong. I added up some antifreeze to the reservoir, because that was low. I cleaned that cap several times, but sludge returns. Did anybody experience this on their Murano, or Maxima, since engines are similar, or do you think they did something to the car while replacing transmission. Is it possible?