Is it permissible for a student to resort to "wasta" (mediation/pull) to obtain higher grades in oral examinations to redress an injustice inflicted upon him, knowing that others might be wronged due to their lack of "wasta"?

It is permissible to seek assistance through recommendation solely for obtaining one's right, and it must be ensured that the recommender will explicitly state that the recommendation is confined to what is rightful. There is no sin upon the one for whom the recommendation is made if others are wronged due to the absence of a recommender for them; the sin lies with the oppressor. If the recommendation will lead to obtaining something that one does not deserve, then it is not permissible, and being wronged is better than being an oppressor. It is advised to turn to Allah for protection from injustice.