when they do the head gasket, they should have changed the oil and flushed out the coolant. if they didn't flush out the coolant and just topped it off afterterward, oil could have already gotten into the coolant. i suggest you flush it out as described in the DIY section...
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"