It really is a terrible design. The cover doesn't line up with the clutch, and you can't see anything peering down through that itty-bitty opening, especially if the oil is clean. If there was ever something calling for a window, the primary is it.

I've never made it, but I've thought about bending some wire into a special T-shaped primary dipstick. Bend it so the top of the T sticks into the adjustment hole in the center of the clutch pack. The other end of the top is held by my hand. The down leg extends along the clutch pack, with a mark at the edge of the discs. Rotate it around until it's down in the oil, rotate it back and pull it out. Look at the oil level.