That's true - (Our) Imam Abu Hanifa (rahimullah) did spend time with Imam Jaffar as Sadiq(ra) and some withhis father Imam Baqir (ra).
True to the Imams sayings Abu Hanifa was loyal to Shaikhain. Imam Malik (rahimullah) did the same I think - but they never became 12ers.
Can you name any Shia scohlar of repute who studied under this two great Imams (ra)?
Ofcourse they did not become 12ers because they started their own schools (fiqh). They did their ijtihad but i am not sure what gave them the authority to only c themselves having the necessary qualifications for independent reasoning in religious law? It seems that the interpretation of the doctrine as it had been laid down once and for all and the doors of ijtihad were closed. Why? Who gave them the authority? Dont you and the ulema of today have the better means of research than them?
And for you now all of a sudden Imam Jaffar as Sadiq (as) has gone from 'performing taqayya' to a 'great Imam'. Good to c u making progress, mashaAllah.
As for naming a shia scholars of repute to have studied under the Imams- Imam Sadiq (as) had time to establish a school and share his knowledge (given that Abbasids and Ummayas were busy trying to kill each other for the Khilafat). Imam Jaffar as Sadiq (as) had over 4,000 students studying at a time!As for the ethical value and virtue of Imam Jafar as Sadiq (as), it is enough to say that none of his students critiqued or found a weak point in his ilm or tadreesh (the ilm was given from Allah (swt) and it was Allah's blessing that they were the fountain head of knowledge).