whirlpool 2000 dishwasher pump buzzing

Hi I have a whirlpool 2000 dishwasher. Its a built in model. Seemed to start a cycle nut then all icould hear was a buzzing sound. I removed it from under the worktop, took off the sides and discovered that the buzzing noise was the motor on the right at the back with an impeller that drives the water into the heater and spray arms. If I knocked it a couple of times it would judder and start to work. If I left it it would complete the cycle, but if interupted the buzzing would start again. I have had this motor out and to my untrained eye the only problem I could see was some carbon dust in and around the impeller, no obstruction, nothing visibly broken.
Do I need to replace the electromagenetic motor or the impellet drive or all of it. Help appreciated.

identification marks on it:

Programe 2000
APD/W2
service: 854593715710
SER: 330410003266
2 years old

Thanks
Pete

Is it a large black pump?

its about ?80mm in diameter...pumps water from inlet to heater and spray arms. front comes off and houses impeller...impeller can be removed and has a shaft about 50-60mm in length and 15-20mm in diameter. Looks like a magnetic shaft. This sits into a housing that is nade up of wound copper wire and has power and earth connections on it. connections are clean and good. dont want to have to replace all parts. does this help at all?

There are two different wash motors for this machine, from your description sounds like yours is a Ceset (metal body). There should be a large capacitor on the side of it. Try another capacitor. The value is marked on it so you don't need to go to Whirlpool for it. If that doesn't cure the problem then it's a new wash pump motor required.
If however you have the large black one, Askol, then you definitely need a new wash pump and motor.

thanks for your help....im sure it said askol on it and there did not seem to be a capacitor on it.
would that mean i have to buy it as a complete unit? Can i only get it from whirlpool? Can you suggest any online suppliers?
cheers

You need a wash motor and pump assembly complete. You don't have to buy it from Whirlpool, try one of your local shops. You'll need the 12 digit number from the label on the side of the door. Should start 85 or something similar. You won't get an Askol pump, the replacement will be a Ceset and it will fit your machine.