Hi guys I know this has been done a million times but I need to get some answers. I just purchased 99 sts with 143,000 and has been maintained well by previous owner. My mechanic said at next oil change I should use Mobil one Synthetic oil and have been reading a ton of good and bad things on this forum. I phoned a GM dealer and spoke to service advisor he said stick to what owners maintence manual is. Has anyone changed and had any problems???
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