Well I just finished renewing, and as usual didn't use a prep school.
As before, the rules of the road exam was straightforward, and the "general" exam was less straightforward. It uses questions aimed at the unlimited Oceans types, some of which is not typical for the 100-tonners--monsoons, ship construction terms, signals shown by a submarine during war games, AMVER message format, tactical circle diagrams, dangerous bulk cargoes, to name a few.
And one admin item that confused me for a while--You'll use the Mariner-number from your license/credential, simple enough. Then, you'll get an Application Number once they get your package. What I didn't realize was you get *two* application numbers, not one: the first is for your physical exam and consequent medical certificate, and I assumed that would be the application number throughout. But it's not, you get a second application number for the License itself. But they don't tell you that up front. So when I got a notice from them using that second number, I didn't recognize it as such, asked them if it was meant for some other mariner. This caused some unnecessary delay. Turns out they were trying to tell me I hadn't paid my fees. But I had. Eventually they believed me, but it took some time.
The other new (to me) thing was sending the renewal (and the fees) to the local REC and not to West Virginia. That's where things went wrong with the payment, at the local office (who had recently been busted for "selling" endorsements and licenses). Don't know how they "lost" my check and Pay.gov info, but they did.
This all made me wish I'd just gone to one of the local license schools--not for the teaching content, but they would have known the new admin glitches, I didn't.
All's well that ends well---finally.