[0]: https://www.navycs.com/charts/2019-military-pay-chart.html
The other thing that can confuse this issue is that Generals and Admirals generally (sorry) keep their titles after retirement. So if you have "Gen. James McClinton" on your board, that doesn't speak to whether or not they're active.
From looking around, it looks like board recruitment efforts toward Admirals and Generals are targeted at those who are retired or nearing retirement: http://blogs.reuters.com/financial-regulatory-forum/2012/01/...
https://ogc.osd.mil/defense_ethics/resource_library/deskbook...
seems like a general with a 40 year career who could (and did) save all of his money could have accumulated a few million dollars in cars without very many shenanigans, if that was their sole financial goal in life.