Great old thread and great job @archibael. I'm starting a 5000X tuner this week so I enjoyed learning about it before I dive in. For anyone else reading this, I've attached a photo of the front end opened up for reference. my Hakko FX-888D had no problem unsoldering the cover. Seeing the whole assembly rather than the close-ups really gives you an appreciation of just how hard it was to replace that Mosfet . . . 
Rich
Rich