Italics have turned to bold

Hello, I’d appreciate some help with 3.4.4; either a link to download the best version for OSX Snow Leopard - 10.6.8, or a fix for the problem I have now since running an Onyx clean up on my system. I have done it countless times over the years with no problem, but sods law has declared that now I am working on a pro proof read, all the italics have changed to bold, and it has thrown in a few other similarly font related issues. Many thanks for any answers.