Still Looks Like Rust But
It really does look (and sound) like rust fungus, but there may be other issues. For example, what did you amend your clay soil with (and we're assuming you planted them in the ground and did not amend the soil and put them in pots)? It sometimes takes quite a bit of amendment to make a clay soil drain well enough for plants like this, that like very good drainage. If the plants are not healthy due to root issues from too much soil moisture and not enough oxygen available to the roots (clay soils can also be very compact and air does not move thru these soils), they will be more susceptible to diseases, even those they don't usually get (but which can infect them). We recommend you look closely at the leaves, especially the underside for the fungal rust spores (orange and/or dark brown to black) and if you find this we recommend you get a fungicidal product (neem oil may be appropriate) and follow the label directions before making application(s). Full sun is correct for these plants and they should be watered when soil moisture is almost depleted in a well drained soil. This may take longer in a clay soil, but in either case, we recommend watering deeply less frequently, rather than smaller amounts of water more frequently. We also suggest you take a couple of stem & leaf samples (sealed in a bag) to your local garden center and try to get a second opinion; provide as much info to them as possible about the care given to these plants. We hope this helps resolve the issue, but if all else fails, you could take another sample (also sealed in a bag) to your local Dept of Agriculture Office and they will usually send the sample to the county plant pathologist and report back to you for free.
