Hi again.
A few final notes from my end:
Stroke could be shortened by inserting a washer of suitable thickness between the rubber bump stop and the mounting eyelet. You could also ask yoyr Öhlins shop to change the schock body, but that might not be economically reasonable... whatever relevance that has on Ducati ownership
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The stock Showa for the S2R singlesides swingarm I bought a while ago looks like this:
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I haven´t tried it out, but it would seem Ducati came to the same conclusion: The stock Monster /ST shock won´t fit.
One possible alternative could be the shock fron the S4R Monster (or whatever the designation for the pearl-white Monster hot-rod was); This is what it looks like on my wifes M800 (not so) Dark (anymore):
Edit: Looks very similiar, the 2. I´ll have a closer look tomorrow ...