"Abbot" (A.K.A. MASTER OF MONK) m4 gbb owner since 2014...
pin problem: Yes. Me too. Extremely tight. But I can put it back.
Buffer Scratches: Mine was very clear (100% new condition).
My m4 ran about 20 mags, the buffer scratches occur like OP.
Hope that helps.
學識 素養 價值觀
勞心者治人
勞力者治於人
治於人者食人
治人者食於人
天下之通義也