Autobarn

Injector seals sit between combustion area and atmosphere, there is no oil at the point that can be introduced, return pipe handles over fueling that has not even entered the injector, again no oil to be introduced ?

Unfortunately all VAG group vehicles use the same style of rubber grommet on the end of drain tubes, whether it is from a sun roof, cabriolet roof or just windscreen trough, in 1999 passats flooded the main comfort control ECU that was in a recess in the passenger side floor due to it, audi TT cabriolets fill the bulkhead behind the driver failing the fuel pump module and EOS models overflow and drip into the car, I can go on forever listing all VAG models, the rubber grommet is pinched together with a thin slot on the end to stop insects getting into them but actually trap crap from getting out, I always chop the last 1/2 inch off with scissors leaving a nice round hole and no further issues.

Reading all these posts even though they do go back two years I am afraid the newer model of Q7 is not as robust as the previous 4L and 4M models, I work on many basic issues on more late models than earlier ones although I have more early models on my books for regular services, some of the components are sourced by Germany from China much like I phone do in the USA, Many, many large manufacturers do this now although they do not publicise it, unfortunately China are particularly bad at cutting corners on metal quality re-using all the scrap they buy from around the world which contains many impurities and results in weakness, I recently diagnosed a stretched timing chain set on a 56,00 mile 2017 tdi which had to go back to the dealer as extended warranty repair, it took three weeks?? and cost the warranty company £12,000. I would recommend anyone with a vehicle newer than 2014 to take out a warranty with RAC or warrantywise or even the dealer, the costs of repair at dealers is going through the roof and expensive electronic components run in to thousands not hundreds. On a brighter note it could be a lot worse, you could own a Land Rover, our local dealer charges £190 an hour and Quentin Wilson who owns Warantywise recently published the top three cars he pays the most claims out on; RR Vogue, RR Sport and Discovery!

Not sure what make the tyre are of if you have found one of our nations many pot holes recently but I had a Q7 in recently with almost exact same issue, the rear tyres were mid range economy brand and one had broken wires in the rubber compound leaving it slightly oval as a result, this is not picked up or effected by balancing but can be found by your tyre guy by fitting on machine and holding a tool like tyre bar or big screwdriver next to tread whilst spinning, if you want to find which one it is yourself, swap one side from front to back, if vibration moves to front from back its the one you changed, if it does not it is the other rear, it is very unlikely to be anything mechanical because the diffs on these are proper not haldex diffs which vibrate for fun

On this model of Q7 there are two lights at top of dash showing compressor activity, one green and one yellow, if these lights are on or flashing it shows the compressor is working to try and make up for lost air, if you let this happen for extended periods without solving the problem it will burn out the compressor, if the front is down evenly on both sides it is not a bag or level sensor, they are independent on each corner at front, the issue is with valve block or compressor, if the comp will not go full lift it is not producing enough air and the front shows it first because Q7`s have active ride level which works harder at front when braking, Compressors range in price from suppliers and on ebay from £189 at Maxspeedingrods to £800 at aerosus for a good reason, "they are all those products are worth" I am curious as to the unit fitted to your truck in last six months. Personally I rebuild all mine using parts from "Bagpipe Andy" inc new head and piston, air dryer and pressure relief valve, you are probably running at about 5 bar and a good rebuild should give you 11 bar. Take a look at the attached pics of before rebuild and available height after and tell me if you recognise the before as like yours

Not possible, Diesel IS light oil so even if you pour something thick like 2 stroke oil in your tank it will dissipate into the fuel leaving no trace, more likely to be other unrefined products from forecourts sourcing cheep fuel during shortages, bitumen is just one of 6,000 products derived from crude but it is more likely to be an organic waxy product that I have come across on more than one occasion recently, not any concern as long as you keep on top of filter changes