Writing the unavoidable, lengthy monologue

My novel is one part a mystery. You're the reader. You're about 40K of 70K words in, chapter 17. The protagonist has finally met the mysterious man with the answers, one whose name has been dropped in every other chapter. They will never meet again.

So I want to write a long monologue. Probably 1000* words. The protag may have a few questions to chime in with but not really, he mostly just wants answers. I think after 40K words the plot should be built up enough and the reader is invested enough that I can get away with it.

Anyone have any advice I should keep in mind while writing it? Am I doing a horrible thing?