<former academic> I've found it helpful to write the letter to the senior researcher. Be prepared to make 4-8 drafts of the letter. The first draft is to just

<former academic> I've found it helpful to write the letter to the senior researcher. Be prepared to make 4-8 drafts of the letter. The first draft is to just dump your thoughts, typically at this point mine are unorganized and incomplete. That gets fixed in the drafts/revisions. The key point is to express my problem/question in the framework which I think the senior researcher uses. And I usually find (? 3 times out of 4?) that by the time I complete this process, I have found the answer to my question. If not, I'll send the email. If they see you've put effort into thinking about it, they almost always respond positively.