Have a couple of 1000 hours on the 500 and never had trouble with the Allison.
We did AG operation, spraying and spreading fertilizer. Really dirty jobs, but thanks to our engineering crew, no let down.
And for the 500: very rugged machine due to the centre frame between front and back seats. I'de rather crash in a 500 than in a 350
"Heck, I can remember when it was Detroit Diesel Allison." Me too
sh.t must be age related.