Is it possible that there is some condensate build up on the inside of the cap where the bimetall disks are? Somehow i can't get it to taste real clean after cleaning in iso - does iso even remove click-missing combustion byproducts?
I continue to find all this concern about 'off-flavors' and 'combustion by-products' and 'can metals be cleaned' to be bewildering: your - or ANY - metal cylinders can be simply and quickly and thoroughly cleaned, as has been laboriously repeated by dozens of thread-members. The ONE real variable is the attention you lavish (or don't) on the process.
ISO, or ethanol, will dissolve anything deposited by your material, combusted or not, in the cap or not; the de-luxe finishing touch is to wash it all in soapy water following the soak, rinse and dry, then run an alcohol-wetted q-tip all around the inside of the bowl, top to bottom, and up the condenser end, wiping the throat of the tip (under-chamber) on all sides. For an assembled tip, this should be all you need to do to keep the thing sweet. For 4 months of heavy use, this has been entirely adequate to keep us all clean and happy.
The washes will remove any and all 'flavor components'; the wiping will remove any traces of physical residue. If that won't turn the trick for you, I recommend adding a round of Oxyclean soaking between the alcohol soaking/wiping and the final wash/rinse. If
THAT doesn't work, I'd advise stripping off the o-rings, popping out the screen(s), then go back to the initial soak & do it all again, this time using a small brush or extra-thick pipe cleanr to ensure that the screens and inside of the tip are completely clean. At some point, you'll find what YOU need to do to be happy with your gear. Don't forget to grease up your o-rings!
Re: the cap itself, if you fill your bowl to the point where the material is touching the inside-top of the cap, then you WILL get a tiny bit of sticky deposit, prolly with a little ash or herb stuck to it, but you're not going to get "build-up" even then: the design of the machine, so to speak, works against a significant deposition there. If the soak alone won't take care of it, the wipe w/ the q-tip after, will.
FTR I have combusted - not lots, but still...yet I've never had a bad taste or even a bad smell linger. IME, those are characteristics of TAR building up, and tar is LOADED with nasty combustion products that will wreck the taste of ANY pipe, which is why we clean them, yes? Even with the occasional burn, there's just not going to be a buildup of combusted materials & byproducts unless we're combusting (nearly) every load.
I soak-then-rinse my condensers and tips without further disassembly, just as in the minimal version of the protocol I laid out; I do it every 2-3 weeks, because I want to harvest the still-potent resin before it becomes laden with tars & degraded byproducts. As a result, I have none of these issues because I get virtually no build-up and so no nasty flavors or smells. It keep my 'Caps clean with minimal hassle, & they keep chugging away, with minimal hassle.
I do expect that at some point, this will allow enough crevice-filling that I'll have to strip the thing down to its components to really have it clean again, but at this rate that could be a year from now, or more....and I'll use this same protocol to do it...unless I find a lower-impact, less-bothersome method than even this one....
Really do hope this helps: I learned the basics of these principles raising a family (and cleaning up after them) and they hold solid here.
Nice stem too, I agree, pairs real nice with that orbiter. 
And there's at least one picture in here of a hole burned through someone's pants...
