Hello99,
I checked the Igros Moshe. It is not as you say. Here are the relevant quotes.
YD 1:45:
?????????? ?? ?????? ?? ??? ????? ??? ??????? ????? ???? ???????? ???? ??? ??? ???”? ????? ?? ??? ?????? ??? ???? ????? ??? ???? ?????? ???? ???????? ???? ???? ?? ????? ?”? ??????
He agrees with the sevara of the matirim, but is only willing to be mattir for bread in a commercial establishment, in conjuction with his earlier sevara.
YD 1:46:
????? ?????? ????? ???”? ??? ??? ???? ?? ?? ????? ??? ??????? ????? ??? ???? ???? ???? ??? ???? ????”? ?? ????????? ?????? ???? ????? ????? ??? ??? ?????? ?????? ?????
Clearly, although he personally would be mattir, he does not do so in the face of the consensus of the Acharonim. (He is also clearly equating other issurim of maachalei akum with yayin.)