Thanks for looking into this @franz. This station C5896 is closest to me, but since it’s no good for Aeris/Rachio’s purposes, I’ll go back to using a different station that is further away (E7923), but does report both values. I had switched to C5896 because recently Rachio started showing the “No Recorded Precip Data” message for E7923.
I suppose I could also try my luck and see if the owner of C5896 would want to try upgrading his firmware 
(as discovered by @petercw2)