Thanks for posting up that external valve - looks like I need to get one!
I recently had my black valve act up - would close easier than it would open. Remote style with the cable. I like the enclosed valves for how they're behind the insulation but not for how much work it takes to get to them.
I had to unscrew a few fasteners and pull down the "fabric" - then the bubble insulation - and there I could see the valve. Sprayed some teflon dry lube where the cable runs and then some grease on what looked like a "plunger" which actuated the valve.
Now it runs smoother, we'll see how long that lasts. 5er is a 2008, maybe I should get ready to replace that valve...