I have read that switching from petrol-based to synthetic oil can affect the engine seals (I assume by that they also mean gaskets), particularly in older cars, resulting in leaking. Now whether this would necessarily involve the head gasket I don't really know, although I rather doubt it. I haven't come across anything, nor do I know, if reverting to petrol oil would reverse whatever effect the synthetic oil may have had.
But just to back up a bit, a closer look underneath might give a clearer picture of what's going on with your car, the p/s fluid would leak from the hoses or the connections, and be somewhat reddish (albeit murky) in color. Oil leaking from the engine would generally be seen along the engine block, maybe some hoses, and be browish or black in color.
Wish I could give more definitive answers. My advice is to forget using the synthetic oil, the benefits, if any, are just too marginal for a '94 vehicle, and petrol oils have advanced significantly over the years as well, and at about half the price. I imagine you wouldn't mind pocketing that change.