We have had loads of these fail (egr position sensor failure) about £350+vat and a pig to fit. too big a job to even try and repair or clean in my opinion. All you will get is your customer coming back with light on again 2 months later kicking off and giving you a bad reputation. vw have done 2 of these under warranty when the car was 4 years old both with about 25/30k on the mileage.
sean