Replaced the diverter valve. No cigar. Gave me a bit more boost and sometimes delays the noise a bit but still there. Also took away my turbo flutter which makes sense but I miss that sound. Anyways. Any other guesses?As to the oil residue; your boost was passing through the bad valve and so, that makes sense. Excess, motor oil, tends to build up in the piping and intercooler overtime. I removed my intercooler, lower hoses and cleaned them out, degreased, pressure tested it for leaks (mine was ok) and it seemed to help my boost performance a bit.