The hot air drying, round plastic disc at the top right hand side of my dishwasher keeps falling off! It can be put back on but every time I do a wash it falls off again. The disc doesn't appear to be damaged in any way and I can't see why it won't stay put!

Can anyone help please, I don't want to pay an engineer £100 to tell me there's an easy way to fix it back on permanently.

Hann, August 2012