Diplomat ADP8322 leaking?

I ave had the above dishwasher for 6 years with no problems until last night, it was started on its normal programme with the supper pots in and during the wash it started beeping. Searching the net lead me to this site, and after reading many replies I decided to have a look myself. I removed the plinth at the bottom and found it full of water, I turned the mains off at the plug and removed the water in the bottom using kitchen towel. I turned the power back on and reset the machine by holding the start button down, and set it off on a rinse cycle, it began to drain then started rinsing, I watched below the machine and water started leaking from the sump. I believe I will need a sump gasket, which I can get hold of. has anybody replaced one?, is it an easy job? Any help would be greatly appreciated.