I've been using a Qtip to put a light coat of Super Lube Synthetic grease on the hinge pin, forend iron and locking lugs of my SxS. Sometimes it gets a light spray of RemOil as well. I tend to use WD40 on the outside as a protectant, but never on the inside.
As far as Big Green goes, mine are all older guns. 870 Wingmaster 20 ga. is old enough that it was built on the 16 ga frame. 870 Express was from one of the early runs. The M700BDL 270 is from 1972 and features a PacNor barrel and B&C Mountain Rifle stock. 700ADL 223 is from the days of the lock on the cocking piece(whatever they called it). It would hardly chamber a round when it was new, the extractor was too tall and would cave the rim in on the cartridge case. Had to grind it down to make it work. Replaced the extractor with a new one and had the same problem. Double checked and there wasn't any trash in the groove it fit in. Guessing the groove isn't deep enough. Talked to a Remington Rep at Sportsmans Wharehouse about it and he answered, never heard of such a thing as he turned and walked away. Never again.