I’ve seen too many people die playing this game, some very innocently relying on people subsequently proven as not competent to be maintaining an aircraft. Based on benjam’s posts I gave him what I consider to be sound guidance. If you’re not certain you know what you’re doing, then get someone who is competent and learn from them. Benjam has proven he is sensible by identifying the RPM drop during run-ups and had it resolved by a competent person. The problem has recurred, so rather than give fixing it a go himself, which is what some seem to be suggesting, seeking the assistance of a competent person is my recommendation.