I have just done a 50hr check and took out the Champion RHM38Ss and put in the Tempests.
The resistance on the Champions (15-25k) did not significantly change since they were measured 37 hours ago (airborne time). This to me suggests that they are as Champion made them, and it suggests that the "megohm"-resistance plugs from 2002 were actually made that way, too.
The Tempest plugs were all around 1.5-2k and I have noted the resistances and will keep track of them at services.
Some funny stuff going on here, and clearly Champion have been having massive long term QA issues but got away with them because most magnetos are powerful enough to flash through the faulty resistors anyway.