i am using the same model for last 3 years and before that had a 2006 idsi. so had been using this model of Honda city since ages. car is always driven on CNG except in cng holidays. the engines of both cars reduced engine oils. initially it was also a concern for me as every one had his own views, tried every engine oil, went to many mechanics. however, took the decision to live with it. engine is still perfect, soundless, mileage is unbelievable both on cng and patrol. so my take on the issue is that its nothing to worry about.