Thanks guys, that all makes perfect sense. I definitely think bench could be the cause of shoulder pain. I usually alternate between DB and BB press (2 splits on one then 2 splits on the other). Chest has always been one of my weaker areas so probably where I lose form the most. I'd be happy just to stick to DB press if it meant less chance of injury, but I guess a lot of the same principles apply to both.
I usually do a lot of drop sets and super sets on arms, high reps with light weights, perhaps with the exception of BB curls and triceps push downs. I do hit arms pretty hard though.