I've been having some fun with a 12 eyedropper that I recently acquired. It's got a great flex nib, which I've never used before. There are a couple of things I don't know about:

1) Is it okay to use 100% silicone grease on the threads? I get traces of ink, but I don't want to ruin the hard rubber;

2) This pen is WET. While I've only experienced the splatter a couple of times, I do notice that quite often ink pools on the underside of the nib between the point and the end of the feed. Is this normal?

okay -- three questions

3) Should I restrict myself to the less-saturated "safe" inks?

This is the first pen I've gotten that's fun to write with.

Yes

WET is OK. Pooling of ink on the underside of the nib is of the time NOT ok.
In some of the wet vintage pens with feeds without fins, it is expected that you get a blob or two when the ink supply is very low.
If you see a clearance between nib and feed, the feed may need to be heat set properly.

No. Use any ink you like. There is no danger.
However, the saturated inks are desirable because of the amount of color they leave behind.
If the ink is very wet there there is a lot og color going to be left any way.
In fact I like weak inks in wet vintage pens because of the extra shading effect they produce.

Thanks for the feedback.

I noticed how vibrant the weak inks are with this pen, and it seems redundant to use a saturated ink. I think you are correct about a clearance between the nib and feed. From what I can tell (with inadequate lighting and a 3x loupe) this is likely the problem.

Thanks again (and I enjoy your videos, by the way)

chances are, once you have sealed up the threads with the silicone grease, you won't have the pooling problem with the nib.