So on my stock 2002 WRX wagon I got my 60K service done at Subaru Stamford earlier in the year. Since then the car reached 79 K or so. All this time I have been getting the oil changed every 3K or so with the last few times the oil coming out pretty dirty and the engine performance deteriorating. Last weekend I decided to do the 75K oil change and when changing the engine oil saw that it was pretty much black in color. On replacing the air filter I noticed that the filter lid was not secured properly. Basically the mechanic at Subaru Stamford had put the clips on one side without locking the far side of the lid in. Long story short the open lid has probably resulted in dirty air constantly getting sucked into the engine for the last 20K miles or so. Any thoughts on how one may go about cleaning the engine internals and sorting this out?