Catalysis of the reaction: 4alpha-hydroxymethyl-stigmasta-7,24(241)-dien-3beta-ol + NADH + O2 + H+ = 4alpha-formyl-stigmasta-7,24(241)-dien-3beta-ol + NAD + 2 H2O.
4alpha-hydroxymethyl-stigmasta-7,24(241)-dien-3beta-ol-methyl oxidase activity