So, I suspected that magneto (I have lightspeed on the other side) timing had advanced and was causing CHT issues over all (not just on #5).
When I took it for an adjustment, I also took off the plenum, just to see if there was anything obvious causing #5 to run a little hot.
Yup, the beginnings of a birds nest. Straw covering the front and back fins of #3 and #5.
I also got the timing checked and it was a bit off...so, all good. !
N430WP RV-10 - Purchased