I switched my engine to synthetic at ~130k, was perfectly fine. It was ran the first 130k/14 years on conventional 5W-30 from the dealer changed every 6 months/5,000 miles. The oil pan gasket eventually did start to weep at about ~150k miles, but it was probably already on its way out. It's not enough to drip on the ground or even down the pan, just slightly damp around the gasket. All I do is wipe it clean when I'm under there doing an oil change and repeat after every oil change. It hasn't gotten any worse. Also, it could be coincidence because I did use two rounds of Auto-RX between the 130k-150k and it may have cleaned the false seal left by the conventional that was run for over a decade.