How tough is it to swap out the trans modulator in a 116?

I have a 450SEL that shifts hard between 1st and 2nd.

I'm assuming it's either the modulator, or the vacuum going to the modulator.

Because the modulator probably has never been replaced, I was thinking of just swapping in a new one. How hard is this to do? I can't find any info on Mercedes trannys.

Thanks