The phrase "now once again" seems perfectly grammatical.  Its interpretation depends on how you want to stretch the meanings of the words, but they don't need stretching.  "Now" is used as one might expect, to contrast the present to the state before September 1991. "Now that the bell is refurbished, it rings . . . ."  "Once" seems to be used with a similar function, but requires the adverb "now" to place it in the present, "Once the bell is refurbished, it will ring . . . ."  The "again" makes clear that we are talking about a restored state: "Now that the bell is refurbished, it rings again . . . ." "Once the bell is refurbished, it will ring again . . . ."  

Hope this helps,
Bruce

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