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Change Back to 0W-40 or Keep Going?

Engine

Model: 996 GT3, Year:2004, Mileage:25,000, Type of use:Street use only
Hi Joel,I have a new twist on an old question I think. My 2004 996 GT3 always had Mobil 1 0W-40 in it but my shop in Los Angeles only used Castrol 5W-40 and during one of the services the Castrol was used in the car. I understand both weights are approved by Porsche. The car then sat a lot over the next two years - maybe driven 100 miles every three months. I had never had any oil leaks or smells with the Mobil 1 but I was also driving the car more at that time. During the two year period of low mileage and with the Castrol in it, it developed a hot oil smell and an oily accumulation in the area normally associated with the RMS or IMS seals - but never enough to drop on the pavement. Now I have driven the car back east (Atlanta) and over the 35 hours of driving, the smell has gone away. I don't know whether the oil seepage was due to the car sitting so much or due to changing to the different weight oil. I would like to go back to Mobil 1 0W-40 as I use this in my 996 C2 - but if changing weights was the likely cause of the problem then I'd rather stick with the Castrol. It is hotter on average in Atlanta in the summer and much colder in the winter compared to LA if that's a consideration. The car has 25K miles on it. I would appreciate your thoughts. Thank you,Mitch Williams

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