I'm bumping this back to life as I have no friggin' idea how I missed this before.
I couldn't even guess how many hundreds of thousands of rounds my '88 vintage 550 has produced and this issue has always been a PIA. Dillon has graciously replaced all manner of primer parts over the years and I've simply developed a routine of disassembly and cleaning of the primer system every 500 rounds.
I just ordered the JW Systems plate off of Amazon (affiliate link above folks ^).
https://www.amazon.com/JW-Systems-Di...gateway&sr=8-1
Thanks for initially posting this @Hambo