Okay, so that's why I went ahead and replaced EVERYTHING that wasn't stainless steel or brass. I'm the new owner and figured I'd start from jump street. Trying to troubleshoot each and every oring failure along the valve as an inexperienced Minimag owner was getting me nowhere. Now that everything is new, if I have a failure, I should be able to track it down as a singular event instead of dealing with several potential failures at once.
Thanks for the advice, though. It'll save me some money the next time around.