Forget The Rain

The Rambam Tefillah (10:9) rules if one forgot to say ותן טל ומתר and they already passed שומע תפילה then they must go back to ברכת השנים.  However, Rav Hai Gaon cited in Rashba  Berachot (29a) rules that one goes back to say it in שומע תפילה.  The question on the Rambam is that the Yerushalmi Taanis (2a-b) is explicit like Rav Hai (see Tosfos Berachot 29b)?  We can understand the law of mentioning ותן טל ומתר two ways.  One way that Chazal instituted initially to ask for rain in ברכת השנים but if it wasn't mentioned then, you ask in שומע תפילה, it is part of the takanah of Chazal.  The other way is that the takanah is only to ask in ברכת השנים, the reason it can be added in שומע תפילה is because it is no different than any other request that can be asked for in שומע תפילה.  Rav Hutner says this is the machlokes between the Bavli and Yerushalmi that Tosfos Berachot points out.  The Yerushalmi holds for גבורת גשמים, משיב הרוח you can also mention it in שומע תפילה.  Mentioning משיב הרוח is not a request, it is a שבח.  So it must be the Yerushalmi holds that Chazal enacted that you can mention rain in שומע תפילה, therefore it says if you forgot ותן טל ומתר, you go back to that beracha.  The Bavli on the other hand holds if משיב הרוח is forgotten you go back to the beginnig of Shemonei Esrai because the Bavli holds mentioning in שומע תפילה only helps like any other request as Tosfos Berachot 29a says.  Hence, if ותן טל ומתר was omitted, it is not enough to return to שומע תפילה, but one must return to its place in the prayer, at ברכת השנים.  That is why the Rambam rules not the Yerushalmi, because the Bavli disagrees.