Leo, the dipstick attached to Mark's oil filler cap was added in about 1980 - before that the filler cap hole acted as a level hole. That is, if your filler cap does not have a dipstick attached to its underside, in theory you are supposed to fill the sump until oil reaches the top of the hole. In practice I find if I do that, when I park the mower after use, it leaks some oil from the filler hole and makes a mess (the filler cap does not usually seal all that well).
