In my experience, RCA caps have never passed the litmus test of affecting sonic character of any prepro or receiver I've owned or tested. However... that being said, over time dust and static and general grit gets on the damned jacks, and I find myself needing the clean the things periodically before something decides to nest in them. To that end, I've used caps that come on f-jacks (ie splitters) and they've worked OK - when they fit, which is about half the time.

Bill O, that's a nice find - cheap and does the job.