I can't tell you if its okt o use synthetics or not, but I would just leave well enought alone. If your current oil is working fine, I don't see any reason a synthetic would be better than what you have. As long as you change it hot and change it often, and don't let it go too far past 3000 miles, you should be fine..
Of course since oil is one of if not the most debated item on this forum, you should get tons of varying answers.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.