David,
The 2002 Marquis has different design bay doors from one side to the other, and that is probable accounting for your different capacity struts. Normally, it is not a good idea to increase the capacity of your gas struts when replacing them because the higher capacity will over stress the mounts. Your struts are just worn out, which is very normal on an 18 year old coach, so replace them with like rated capacity and size. The problem arises when you get a used coach that has had some of the struts replaced with the wrong struts, All doors of the same size and hinge design should have the same strut.
Gerald