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Mrs. John Giblin of Cleveland, Ohio mentioned in Reuben's obit appears to be Helen M. (Daisy) Giblin, nee Roach.  https://cpl.org/newsindex/showrecord/?record=516050&type=necrology&searchType=both  Not sure why there's a different last name for her than McDonald.

The Butte Co. library will do look ups in the Oroville paper.  https://www.buttecounty.net/600/Obituary-Newspaper-Article-Request

The date of birth on the marriage license to the marriage with Hilde seems to fit what you have.

This looks like the correct passenger list, as the place of birth is Mayen and the 2nd page has father Anton - https://www.familysearch.org/ark:/61903/1:1:QVPZ-H7L3

There are entries in the indexes for petitions for naturalizations for Hilde & Henry Mondorf of the right dates of birth from 1950 in the US District Court in NY City.  They were living at 311 E. 93rd Street, New York, NY. 

The Social Security Death Index says he died in Oct. 1978, and his last residence was New York City.

The Minnesota death index shows the Victor who died 17 Apr. 2006 as having parents William Johnston & Hannah Brusch, and it lists the informant as his daughter.

If that's the right date of birth on the naturalization & WWII draft registration, it looks like Henry died on 5 March 1977 in New Jersey. 

Social Security death index:  https://www.familysearch.org/ark:/61903/1:1:JBTJ-MT1

New Jersey death index: https://archive.org/details/NJ_Death_Index_1977_G-N/page/n451/mode/1up

Obituary:  https://www.newspapers.com/article/press-of-atlantic-city-obituary-for-henr/148107355/

The marriage license for the 1939 marriage to Hilde said he was not married previously   :  https://a860-historicalvitalrecords.nyc.gov/view/11265160

I don't know if the children of Henry mentioned in the census are deceased or not, so I may have to remove the names.  It looks like the daughter mentioned in his obituary passed away last year.  Her obituary had no mention of siblings one way or the other.  http://www.rootschat.com/links/01t74/