menappi,
The old myth about swapping synthetic and organic oils is just that, a myth. Most of it comes from the fact that many synthetic oils (RedLine for example) have an excellent additive package that will actually help clean out the inside of your engine. Back when these oils were first becoming popular, say in the early 80s, there were some seal problems that caused leaks...I wouldn't worry about it now at all...after all, they do *blend* synth and organic oils, right. I've also swapped between synth and organic in my CRX without problems.

Without knowing what kind of oil is in there, it would be difficult to tell, even from a used oil analysis exactly what's in there...I'd say it's not too important. Use whatever oil you want that is the proper grade for the engine and environmental conditions and you should be fine.

Bogatyr