Gradually is giving poor results particularly stuff on the lower shelf, Cutlery and plates are ok but pans and dishes are starting to come out still dirty. I feel the problem is a restriction in the internal pipework to the bottom impeller but what to do about it.
In Spain where repairs are difficult.
The bottom spray arm just pulls out, the top is held on with a bayonet spindle that twists counterclockwise to release. What may be a possible issue is if the water diverter is jammed? The symptoms for that are often than one basket cleans OK but the other doesn’t….maybe that’s what you are finding?