Tobias, as far as I was able to determine, the coil element is the same. I think the pattern differences were due to the aluminum casing that goes around the element in the 409 that is not present in the 408. I used one of those 408 elements to replace a defective one in an older MD409-N, seating it inside the aluminum housing. I haven't measured it with a scope or anything, but in A/B comparisons, it's practically identical to my MD-409-U3s.
I know the Sennheiser paperwork shows the pattern differences between the capsules, but I'm curious if anybody still there had any experience building or designing the two. I mean, I may be wrong, but I'll be shocked if the difference between the two capsules is anything but that aluminum casing.