I'll try to help. Also search this forum for "HIV transmission risk", "oral sex", and "fellatio" for more detailed discussions--some of which in fact have been quite generalizable.
1) The most commonly cited figure is 1 chance in 10,000. The true risk undboutedly varies widely in various circumstances. Most likely it is much lower in your circumstances, and higher with intra-oral ejaculation, gum disease, oral or penile lesions due to herpes or syphilis, etc. Your "all it takes" statement reflects a general misconception about HIV infection. In general, getting HIV requires large doses of virus, not just "any exposure".
2) The biological reasons HIV transmission is uncommon by oral sex aren't fully understood. Not all mucous membranes are equally susceptible. For example, the linings of the rectum and cervix are only one cell layer thick, compared with much thicker oral and vaginal membranes. Saliva contains HIV inhibitory substances. Even swalling HIV doesn't usually result in infection.
3) Condoms for oral undoubtedly would reduce the very low risk to zero, and some people use and/or recommend them. Public health officials shy away from such a recommendation because in the long run, it wouldn't prevent very many infections, and because there is fear it doesn't pass the "laugh test". People might say "If I have to use a condom even for oral sex, I just won't use one at all"--even for anal or vaginal sex. That could have the effect of increasing overall risk.
4) Jeff Klausner would agree with me that if you focus on professionally run website, and especially those where public comments are medically monitored, you'll actually see a pretty consistent perspective. Personal testimony from individuals about how they (or a friend) got HIV are the least reliable of all evidence. That's not to say it doesn't happen; it can and does. But the ones most likely to contribute to online conversations are those who believe it happened.
If all anal and vaginal sex could be abolished from the world and only unprotected oral sex remained, HIV would die out. Oral sex, either fellatio or cunnilingus, in either direction, simply is not a sufficiently efficient transmission mechanism to sustain transmission of HIV in any population.
I hope this helps. Good luck-- HHH, MD
You are right when you say the post may help other users, I had similar questions. However I notice mention is made of saliva properties but I can't help but wonder about cuts on the outside of the mouth (cracked/split lips etc) which could get vaginal or semen fluids on/into them & which I assume would have no saliva protection.
Thanks for your time and detailed information. I did do a search in the forum - thanks for the tidbit. Would you put oral sex risk in the same category as protected anal sex or protected vaginal sex?