Paola, Thank you so much for responding!From the name you have given, I would say the original German name was possibly Theophilus Ferdinand Seyffert.I searched with both "Theo.." and "Ferd.." as given names for "Seyffert" at the Mormon site, familysearch.org, but received nothing to indicate that they have his birth, baptism or marriage record in Germany.That is not too surprising, as it is my understanding that Kingdom of Saxony records generally have to be researched in person at the German archival center for the state of Saxony.
Have you tried looking in local or regional library collections in Mexico to see if your great uncle may have donated either some of his papers or a self-published genealogy to a place of safe-keeping?Sometimes family researchers do this, and the surviving relatives either don't know of it or forget to tell the younger generation of it after the researcher's death.
Also, is there a possibility your ancestor would appear in a census?The Mormons have (at familysearch.org) a searchable database of 1880-81 census information for the United States, Canada, and the British Isles, but I do not know what Mexican records may be available in like manner.A census record would at least give you an idea of the time period of your Teofilo's life.I suspect he came in the 1850s, plus or minus a decade or so.
About 15 years ago, I met the president of the university at Cd. Juarez when he visited Kansas City.The man's first surname was Campbell, and I had to ask him about that, of course.He told me that his paternal ancestor was a young Scottish mining engineer who came to northern Mexico and married a local girl.European immigration into the area was not so unusual, and others who have such ancestry may be able to give you advice as to sources to use in documenting your German heritage in Mexico.
I will try to contact you off-line now with still another idea I have for your research.Best wishes!Gordon