Go and buy them at the Auto Part store and then go and check and see if they match the one's at the Merc dealer if they do then just put those on. $49.00 !!!! Maybe he read it wrong and it's $4.90??
P.S. - You could buy gasket material they sell it in rolls. And then just cut it with a box cutter to the shape you need. I've done it before for other types of gaskets (i.e. Water neck) Worked fine.