Been with me since season 3, Robin Poirot: Attachment 23214 I'd forgotten he started as an MC, until I went back and looked at his old pix. I don't intend to sell him, since I did have to sell Hannasyde this season, another I had since then. :D
Also deserves an honorable mention
(since I do intend to keep him but who knows)
Daniel Kwoczala has been with me since Season 4: Attachment 23215
And of course the star of the team: Attachment 23216
I think this in category of record my team does well. Since I train them a lot I keep my guys long term. Which is a good thing 'cos I get attached to them. :D