Hotpoint FDW60 help please

Hi – I have the above model and its been a good servant – i recently replaced the heater and its had a new lease of life.

I noticed the other day that stuff wasnt being cleaned to its usual standards – i tried another couple of cycles and it was taking in water and draining fine – the water was also nice and hot but the one thing i noticed was the upper spray bar had a lot of play in it. I’m thinking as its spinning round while expelling water its catching the tray and just not pushing the water around sufficiently to clean perfectly. I also noticed that the tablets havent been fully dissolved either. I had a look at the upper spray bar and it has the nut with the black seal and also another clear washer/spacer but this is split and missing a quarter section of it. I have looked at spare parts and you can buy the nut or the spray bar but i can’t see any reference to this clear washer/spacer and it looks like this is the bit that keeps the arm running smoothly!?? Is it possible to get this small part on its own or if i need to buy the nut does that come with it?