Cleaning out residue from thread of sport mixer base

I am talking about the following accessory:

The problem is that in the thread (i.e. the "cracks" onto which the bottle is screwed on when blending the fruit) some fruit remains got stuck. No amount of scrubbing with dish soap/sponge and rinsing removed them so far (they just get wet, maybe even loosen up a bit then dry out again; maybe it is even worse now, because now it is fruit remains soaked with dish soap, which could end up in the fresh smoothie...).

Although I was able to winkle this residue out partially with the tip of a knife, I am looking for a better solution, because that way is neither effective nor perfect (I think about 40-50% of the residue is still there, and it is a pain to do this process anyway).

Long story short, the problem is that the thread is too tight and too deep to effectively reach and clean out with the usual means.

So I have basically two questions:

• is there some effective practice to remove this stuck and dried residue? (I was thinking about soaking it into vinegar, but maybe that would damage the unit too? E.g. make the knife rust, or remove the lubricating oil from the shaft. And I'm not sure it would even remove the residue in the end...)
• is there a way to prevent this residue from forming in the first place? (Like soaking the base immediately after use? But again, won't that remove the oil from the shaft?)

I tried to do some research, and I found the suggested way of cleaning out blenders is to put water and some dish soap in it, turn it on, and let it do the rest. But I don't think it would work in this case, because when the blender is running, this thread is theoretically sealed by the bottle which is screwed on. (Which is a good thing by the way, because in this way, in theory, the residue can't get into the fresh smoothie. On the other hand, the question arises how did it get there in the first place then?)