There is an o-ring under the screw head that secures the lever onto the barrel.
You might want to obtain a spare in case it's damaged, before you fully service the DSV.
Tribolube seems to be allow far smoother operation and doesn't clog like christolube.
I was taught how to disassemble, clean, lube then re-assemble the DSV as part of the Meg MOD1 course.
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