Anybody still using 30 weight CJ-4 oil in a Navistar 7.3L IDI

I’ve run 15-40 delvac in my 93 idi for the last 200k miles…it’s got roughly 400k on it total I don’t know what the previous owner used but the 15-40 can’t be too bad for it
Case/ih farm equipment used to have a love affair with 30wt might try your local farm equipment dealer