If your dishes are not being cleaned sufficiently and the upper spray arm itself seems to be fine upon inspections, it may point to a problem with the feed pipe for the spray arm.
ForMySpares can be of help with this genuine replacement upper spray arm feed pipe that will drastically improve the performance of your dishwasher.
Genuine spare part for select models of Smeg, Diplomat and CDA dishwashers.
Please check the suitable model fit list to ensure that this is the correct part for your appliance.