Does small amount of precum on outside vagina(vulva) can transmit hiv?

Possibly: There is certainly a risk, though less than other circumstances.

Sure: If your partner is HIV positive and you were exposed to his semen then there is a risk of transmission. You should be tested. If he does not know if he is positive or negative then he can get tested too.

Unlikely: But as recipient you have higher risk. Only if he has hiv?

Low risk: There is no risk if the owner of the precum is not infected with hiv. Even if the precum donor has HIV and you have no skin lesions like open sores, the risk is minimal. If you washed the precum right after it was deposited you would have little risk. However, your list of conditions includes hiv, if you have HIV you should get treated immediately as treatment can improve health.