Stripping down my L579 receiver for a good ultrasonic cleaning and re-oiling. I use a mix of kerosene and acetone which dissolves hardened goo quite effectively! There's some fine roll pins and springs in the No 4 trigger assembly that I'd rather leave in place, and the ultrasonic does a great job of cleaning every last crevice. I then blow out with an airgun, final degrease with Brake Kleen and re-oil using synthetic auto transmission fluid, thin enough to soak into all the newly clean crevices and stable over a wide range of temperatures. One thing struck me on re-assembly... while there are clear instructions on adjusting the No 4 weight of pull and over-travel, the protrusion height for the upper grub screw is not specified. Dimension AA is what I need to check... seems to be 1.4mm or so, and sets up the amount of engagement between the trigger cocking piece and the bolt striker. Apparently later A series No 4 triggers replaced the set screw with an integral standoff boss on the main housing.