I own the S-51 as well, and love it for what it is - but beware the frustration of arty as you have little hope of saving bad teams from themselves. I went 3 for 3 losses today when, especially in two of them, I could do no wrong with my hits (insta-killed a ST-I, their best tank in a tier 9 match, early, plus two more - yet we still lost the first game).
The S-51 has splash damage like you've never experienced if you haven't played higher tier arty on other lines, so as a safer default - like these guys said - aim through them, not down on top of them.
But just as my GW Panther went, this awesome arty may have to go, too - I refuse to keep watching my high tier tanks do stupid stuff when I either can make it (if anyone would spot past the half-way line on the map), or already made it, so much easier for them.
There are just too many drooler pubs playing to give up a top-tier heavy slot to them so that experienced arty can enjoy their roles anymore.