I put plated steel plugs in the last race motor. Always ran with distilled water and water wetter. It did OK for a year or so, then a plug sprung a tiny pinhole leak one day at the track. I pulled it out and the back was badly rust pitted. I put a rubber expansion plug in and, went back to racing. Next event, another plug went and I put another rubber plug in. After that, I went home and installed rubber ones in the other 4 holes. Ran it for another couple years that way never a problem running a 21 pound cap. Heck, I even thought about putting 'em in the current engine but, went brass. I do keep a couple rubber plugs around for backup
