I've got the same problem with the driver's seat on my 1998.5 Contour GL. It also is a manual seat. It felt like the seat bolts were loose. I tighten the bolts down, but the seat still moved from side to side. I finally looked under the seat pan and found that the brace piece towards the back had sheared in two. The entire seat pan needs to be replaced (approx. $250 for the pan!!!).
I think I'll call the local dealership tomorrow and ask about a replacement. The car has only 66,000 miles on the clock. The seat should not have come apart like this.
