I have a Honda Prelude which has an H22. The reco'd oil viscosity is 5W-30 and 10W-30, varying by ambient temp. The S2000 uses an F20/22c. That engine has 5W40 (all temps) and 10W30 (above 0) viscosity recommendation from Honda. Since the H22 and F20/22c have extremely similar critical clearances (crank, cam journal, oil pump) and also since the F20/22c has a 10W-30 warm weather reco like the H22, can I assume it'd be within the design parameters of the H22 to use 5W40 in it? The only main difference between the two engines is that the F20/22c uses roller rockers. The reason I'm asking this is that in the last few years cam/rocker failures have started popping up in the H22's (stock valvetrain). Many suspect a potential ZDDP oil deficiency problem. The M1 5W-40 oil seems to have a decent amount of it, and I'd like to use it if it makes sense to. Any thoughts?