My bad... I just realized that the affiliate list from a Japanese AT40 fansite I was looking at online only listed stations that STREAM AT40 - and it also was not a complete list. Sorry for the confusion.
According to other sites I've visited, other AT40 affiliates in Michigan currently airing the show include WKFR 103.3 Battle Creek/Kalamazoo and WIOG 102.5 Bay City/Saginaw/Midland/Flint (both CHR/Pop). WKHM-FM (K105.3) in Jackson also airs it, according to their website, though I'm not sure if it's the CHR or Hot AC version (probably the Hot AC since their general format is Adult CHR). During my college years (1998-02), K105.3 aired Casey's Hot AC Top 20.
In northern Michigan, WKPK 106.7 FM (The Peak) Gaylord aired Casey's Top 40 on Sunday mornings in the mid-1990s; I remember listening to it one Sunday morning as I was getting ready to go home from a weekend up north, and it was a treat getting to hear it since I lived in the Detroit area which did not have a true CHR at the time. By 1997, IIRC, WKPK had dropped it and the show moved to competitor WKHQ 105.9, which I believe still airs it today. I also remember hearing Casey's AC countdown when it was still a top 20 on WLXT 96.3 (W-Lite), WKHQ's sister station; they aired it Sunday evenings.
WVKS 92.5 Kiss-FM Toledo has aired AT40/Casey's Top 40 for as long as I can remember; I used to enjoy DXing them from the northern suburbs of Detroit on Sunday mornings when I was in high school.
I have heard old airchecks of WHYT 96.3 featuring promos for AT40, so I can confirm for sure that WHYT was airing AT40 in 1983-1984.
Going farther back in Toledo, I think WOHO-AM 1470 (now WLQR) aired it in the early '80s.
I also have heard that CHYR-AM 710 Leamington, Ontario, which had a strong signal in Detroit, aired AT40 during the 70s and 80s, and I think I remember WDFX-FM 99.5 (The Fox) airing the Shadoe Stevens version of AT40 in the late 80s and early 90s (by then WHYT had gone very heavily Rhythmic and had dropped Casey's show, IIRC). Someone correct me if I'm wrong on this.