... or is there some myth about synthetic prone to leaking?
It's no myth. Seals absorb oil by design; it helps them swell up to do their job. It's no problem changing to synthetic in an newish engine (say up to 45,000 or 50,000 miles). After that, changing from mineral to synthetic can result in leaks. This is thought to be due to the synthetic oil driving the mineral oil out of the seals, and the seals contracting slightly due to their age. Why the synthetic doesn't swell the seals back up again is not explained, but maybe it's the smaller molecules?
So, if your vehicle mileage is on the low side, change to synthetic without fear, and then stay with it. If not, better not risk it.
