The risk is extremely low and to put it another way, if there was exposure and you were exclusively on Shell and could prove it (receipts), they would be deemed as being liable. The other issue that you would have to prove is the lubricant that you are using and that you change according to recommendation.
To reassure you, before a new fuel package or lub is announced, it undergoes multi-testing regimes with both dynometers and live tests and both for short term benefits and long runs - maybe up to 150000 miles and in several climes - taxis are good test beds for the endurance testing. Shell takes this extremely seriously - yes, occasionally things go kaibosh such as with the launch of Formula Shell in the 90s when they had issues with Porsche and VWs coming to a halt - not so good for the Dutch motorway police. However, there they withdrew the additive for an older one, reformulated and tested and it was out of the consumer mind within 6 months whereas in the UK, they made the mistake of withdrawing the brand and ending up with confusion of the difference between 'Formula' and 'Advanced' - I saw the mkt research behind this.
Such testing programmes are almost as rigorous as drug testing programmes, partly as the car is our 2nd biggest spend after the house. The States, the EU/UK/Germany/France/Sweden and Japan all have separate test protocols to sate before international launch, reflected in all the different type of specifications ascribed to the fuel/lub.....
Residues are far more likely with poorer quality fuels and are usually carbon sludges, the detergent to loosen and take to the filter or they are burnt off with high temp, such as with the enforced acceleration I described earlier.
There are always the doubters as we in the industry know and a lot of effort to get things right is taken!