I just had to replace the valve cover gaskets in my 2004 Grand Caravan with 162K miles. Imagine my surprise when the mechanic informed me that the 3.8 liter engine had 1 steel cover and 1 plastic cover. Has anyone else seen this?? That also meant that we had to order two gasket sets to make them fit onto the covers. I’ve owned this van since it was new, and never had the valve covers off.
A little checking on Rock Auto provided a clue. They only list steel valve covers for 2003 Grand Caravans and only plastic ones for 2005s. The 2004s came both ways so my guess it was changed from steel to plastic sometime during the model year. When it was time to put the covers on your engine there was only one steel one left.