I was reading a gay mens magazine in the clinic waiting room today (..) and it said that the risk of getting HIV/AIDS from oral was 3% but you need to take into account how more often people would like oral etc...
Oral is the almost universal sex act between men, so the HIV risks for oral have been studied for ages. Ghod knows where they got 3% figure from - that's the top end for being on the receiving end of bareback anal with an HIV+ man.
For oral, the top end estimate is 0.04% (4 in 10,000) per CIM with an HIV+ man. Personally, I think that this is an over estimate - the study it came from made some assumptions I think are wrong - and there's evidence saying the risk is somewhere between nil and almost nil.
If you do OWO but not CIM, the HIV risk is nil.
There are other things you can catch. Whether or not you do OWO depends on how you balance the risks and rewards: personal, professional and medical. There are loads of threads about it here, because it is one of the classic 'some people do, some people don't, it's totally up to you' issues. If you do it, make sure you let the clinic know so they include throat swabs.