This Sedin splitting is not going well for Daniel. It was always known but now I think it's really really obvious that Daniel needs Henrik more than Henrik needs Daniel. Put the Sedins back together, and trade the first round pick + Jensen + other small pieces if necessary for Vanek.
Daniel is a goal scorer and he needs a playmaker and Henrik is the only playmaker we got.
Aside from that, if you do a binomial distribution for 18 goals on the last 212 shots (which I believe is what Daniel has done over the last 70 regular season games), the confidence interval is 5.1% to 13.1%, which encompasses his 12% career shooting percentage.
The conclusion is that you can't say that Daniel's true shooting percentage has actually declined.
Looking at the numbers a different way, a 12% career shooter can go through 70 game periods where they take 3 shots per game and score anywhere from around 16 to 36 goals.
This is nearly the flip-side of his 2010-2011 season. His expected range for that season was around 22 to 44 goals, and he ended up near the top end for that. Both that season and this latest 70 game stretch fall within the confidence interval ranges for a 12% shooter though.
Shooting percentage doesn't tend to fall too drastically with age. Naslund was still an 11% shooter in his last season with the Rangers. Usually declining SOG is more of a signal of trouble.