Hopefully i can help..
What colour is this substance your seeing here?
Was this an issue before you had the underside done - what was the reason surrounding having done in the first place?
Hi, I just bought the car 2 weeks ago. The colour is clear. Looking in my rear view mirror I saw the rear window smearing over. It cleared after using wiper . when I reached my destination and opened the boot. It was oily over my hands. Could not smell diesel. the reason I had the underneath done was to give protection to the underneath on advice from my brother.
Hi..there thanks for your reply..
Ok..If it a clear substance oily as you describe and isnt black for it to be engine oil..then its possible the oil wax you had done under the car is the cause..especially so if this wasnt an issue before hand..Diesel leaks should be really easy to spot and smell as it doesnt tend to disappear like petrol aswell as that on a wet ground surface you would see oily film traces under the car if it were a diesel leak..Being 2008 model its not really nessesary to oil wax or wax oil the undercarriage.as they have there own protective coating anyway thats last a very long time.its kind of rare for anyone to that nowadays even undersealing especially on a newer car anyway..if this coating you have applied under the car is still wet or due to the heat of exhaust system which does get very hot being a diesel maybe melting somewhat and the forward motion of the car is causing that oil to build up over the back panels/boot/bumper etc. that could be your problem..have look right under the car in particular right in behind the bumper and boot floor area and have a look and see if there is build up around there..if the film trace is the same smell as that applied wax oil - and isnt diesel / engine oil / brake fluid related then the wax oil/oil wax will be your problem..I do hope this helps