I recently noticed oil in the coolany reservoir and took it to a reputable shop for repair. They replaced the pcv valve and flush the coolant system. They were upfront and said that they were not certain if this would fix the issue and several hundred miles later the issue has returned. It has approximately 110,000 miles and the CVT fluids were changes about 10k miles ago.

I've read it could be many issues from a heat exhanger unit, upper oil pan o-rings, oil-to-water cooler (oil cooler?) to a blow head gasket. There is not coolant in the motor oil and I'm asking to see if there is a most likely item to check next. Also, is it safe to drive short distances?

Thanks in advance for any information or insights into this issue.