The hadith "Seek Knowledge even if you have to go as far as china" is fabricated and does not exist. The actual hadith is:
The Messenger of Allah (peace and blessings of Allaah be upon him) said: ‘Seeking knowledge is obligatory upon every Muslim.’” (220. Classed as saheeh by al-Albaani in Saheeh Sunan Ibn Maajah)
I can confirm this from our local imam as well who said, he had read many hadith books but could not come across this one. Another reference is is here - Islamqa.
There are in fact other hadiths as well which were fabricated. I dontdon't think they were fabricated with ill intentions but merely they enhanced the positivity of a hadith or event.