Volvo recently issued a recall for the 850 stating "after prolonged exposure to extreme heat, the fuel tank in model years 94-97 850 vehicles may develop seepage at the heat shield attachment. This is because the heat shield attachment location may not meet certain Vovlo specifications. When this occurs, a fuel ordor may be present." Volvo will check the vehicle for seepage and replace the tank if necessary. To prevent future occurence of fuel seepage a bushing to each of the heat shield attachments will be installed by Volvo.

Granted this is different than your problem, but could be along the same path.
The campaign notice was issued Feb 2005.

Dave
96 855R