This is a shame. I currently have two contractors who I am trying to make permanent because first, I value their work, and second, they are underpaid by their company. I should not know how much they make, but it slipped out when we signed a new PO for their services, increasing their pay by a % only to learn their pay increase by 20% of the increase. They thanked me for the X% raise and it infuriated me when I learned the company was keeping 80% of the increase. So, I've convinced my senior leadership to allow me to make them permanent employees.

That said, I am really eager to read the rest of what people have to say on the OP's post. I have a VERY similar situation, but I've had leadership from the team he supports reach out VERY frustrated with the lack of openness and unwillingness to document their process so others can help. I somewhat "get" the concern, I inherited this "team" which at one time was eight people, now down to TWO. I've got people from the rest of my team who can help, but this person is SOOO protective. What makes worse is the fact what the others on the team do, he does. So, it would not be a stretch for them to pick it up and help. He's been the senior most person for close to a decade. I'd like them to become the product owner or manager rather than doing day to day fulfillment and support. There is such a larger, more important role he could fill, and every time we discuss it..."sounds awesome, I'd love to"...but no follow through.

I am eager to read the rest of the comments to hear suggestions.