All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
In fact, Hajj is not invalidated by discharging pre-ejaculatory fluid. The questioner has not clarified to us what he intends by his being in front of the Ka‘bah: does he mean that he was sitting in the Sanctuary in front of it or that he was performing Tawaaf (circumambulation). If he was performing Tawaaf, then was it Tawaaf Al-Qudoom or Tawaaf Al-Ifadhah? He has not clarified either what he intends by his saying that 'he felt' this: was this feeling mere suspicion, or did he think, almost certainly, that the pre-ejaculatory fluid came out he detect its traces afterwards? All those are but probabilities, and it would be too lengthy to discuss them all.
Anyway, we can say that the discharge of the pre-ejaculatory fluid nullifies the ablution, and if it comes out during Tawaaf, then one should leave the Tawaaf and purify himself from it and then repeat ablution once again and start Tawaaf all over again since purity is a requisite for the validity of Tawaaf according to the majority of the scholars. An exception is made if the pre-ejaculatory fluid comes out so frequently that it is difficult to purify oneself from it every time. This case takes the same ruling like urinary incontinence, and ablution is not nullified because of it.
Allaah Knows best.