Both the 30D & the 20D definately have dip sticks (and as the 35D is the same block, I am sure it also has a dip stick). I understand that some of the petrol engines do not have dip sticks.
I had the pleasure of showing the technician where the 30D dip stick is after he swore blind that there wasn't one.
Lift off the sound deadening top cover.
Behind the air filter to the right is an oval black knob.
Lift it and lo and behold it is a dipstick.
Seach the forum and there are pictures of it - Lotus7 I think