Old packing makes things difficult, seems like it’s more stubborn when it has a lot of hours. Also, you might have the old style stinger (Rotax updated it) that tends to break at the furthest end. I’ve been through several, so I feel your pain. Once I upgraded to the new style (read: better built) stinger I haven’t had problems. Unfortunately your best bet is to just pull on it until it comes out. That old packing might be stuck to the walls of the pipe, so you might need something long you can stick down In there and hook on to the packing.
Tip: Stick a sticker at the end of the pipe closest to the U-bend. When the sticker starts to discolor, it’s time to change the packing.