I play mostly space master (2nd ed) which is essentially old school RM. Similar mechanic - the SM skill has a SD modifier (in that edition stat bonuses were much larger - I have a telepath with a SD modifier of +50 due to race and stat), and everyone gets +3 per level, in addition to any level bonuses they may have (forget if it's in combat group or concentration). -10 per round of accumulated stun, doll OED, break 100.
So a 5th level character stunned for 5 rounds with a +10 SD mod would be at +10 (stat), +15 (level), give him a +2 per level other level bonus for +10, -50 for accumulated stun, so -15, plus any developed ranks, to break 100. This is in a game with weapons specifically designed to stun you, and in Space master, first stun usually = first death soon after. Especially since it's hard to take advantage of your half OB for parry option when all you have to parry with is a laser pistol and they are shooting a machine gun at you.
Which actually reminds me of a question that has nagged me for years, which I'll put on the SM board